Combine: throttle and debounce

Updated March 2020 with more thoroughly accurate timing diagrams, after vetting against iOS13.2, iOS 13.3, and iOS13.4 beta.

Combine was announced and released this past summer with iOS 13. And with this recent iOS 13 update, it is still definitely settling into place. While writing Using Combine, I wrote a number of tests to verify and generally double-check my understanding of how Combine was working. With the update to iOS 13.3, the tests showed me that a few behaviors changed once again.

The operator that changed and trigged my tests was throttle. Throttle is meant to act on values being received from an upstream publisher over a sliding window. It collapses the values flowing through a pipeline over time, choosing a representative value from the set that appeared within a given time window. It also turns out that throttle has slightly different behavior when you’re working with a publisher that starts out sending down an initial value (such as a @Published property).

While I was poking at throttle to understand how it changed, I also realized that debounce was acting differently than I had originally understood, so I took some time to write some additional tests and make a more explicit timing diagram for it as well. Since debounce didn’t change behavior between 13.2 and 13.3 (that I spotted anyway), I’ll describe it first.


When you set up a debounce operator, you specify a time-window for it to react within. The operator collects all values that come in from the publisher, and most notably it resets the starting point for that sliding time window when it receives a value. It won’t send any values on until that entire window has expired without any other values appearing. In effect, it’s waiting for the value to settle. The marble diagrams show this really well.

Without a break that lets the sliding window expire, a single value is returned.
With a break that lets the sliding window expire, two values are propagated.

When using debounce, you will see a delay invoked between when the event was published and the time it is received by your subscriber that is at least the value that you are processing the debounce across (0.5 seconds in the above example).


Throttle acts similarly to debounce, in that it collects multiple results over time and sends out a single result – but it does so with fixed time windows. Where debounce will reset the start of that window, throttle does not – so it doesn’t collapse the values entirely, but sort of “slows them down” (and that matches the name of the operator pretty well).

Which value from the set that arrive that’s chosen to be propagated is influenced by the parameter latest, which is set when you create the operator. In general, latest being set to true results in the last value appearing getting chosen, and latest being set to false results in the first value that appears. This is one of those items that is a lot easier to understand by looking at a marble diagram:

Throttle (latest=false), under iOS 13.2.2
throttle (latest=true) under iOS 13.2.2

The notable behavior change is how it handles initial values. Initial value seems to be a bit “flexible” in what is specifically initial though. When I first wrote my tests, I was using a class with a @Published variable, which sends a value upon subscription, and then updates when it is changed. To illustrate the 13.3 behavior change better, I re-wrote and expanded those tests to use a PassthroughSubject, so there wasn’t an automatic initial value.

throttle (latest=false) under iOS 13.3
throttle (latest=true) under iOS 13.3

So under iOS 13.3, the initial value (which is sent out roughly 100ms after the creation of the pipeline in my test), is always propagated, and then the sliding window effect begins immediately after that.

When using throttle, you will see almost no delay between when the event was published and the time it is received by your subscriber. In the tests where I work the timing, using throttle with latest=true shows almost no delay, and throttle with latest=false with a very short delay: 20 to 40 ms in my test environment. debounce, by comparison, will always include a significant delay.

If you want to see the underlying tests that illustrate this, check out the following bits of code from the Using Combine project:

Using Combine (v0.8) update available!

A new version of Using Combine (v0.8) is now available.

The live HTML site for Using Combine is updated automatically, and the PDF and ePub versions are now available on Gumroad.

This version has a number of additional notes and changes, primarily from reader feedback, and some references to Combine’s changes with the release of IOS 13.2. A few more issues have been noted in the book, along with references to feedback reports sent to Apple where they may represent bugs or unexpected behavior in the current implementation.

This release also includes SVG based diagrams – so the original ASCII art diagrams are now gone, which should make that content far more accessible in the ePub format.

In addition, I added a section on marble diagrams, specifically in how to read them and how they apply to the code and examples illustrated in this book. I originally planned on generating all the marble diagrams, but after repeated efforts at that I backed off that idea and am creating them by hand, with the help of OmniGroup‘s wonderful tool OmniGraffle. And yes, the source for this is also in the github repository.

For the next release, I am planning on getting back to detailing out the as-yet-unwritten section on a number of operators. 

The project board at also reflects all the various updates still remaining to be written.

A huge thank you to all who have supported this book and my efforts to provide it!


A torii gate at Danjo Garan in Koyosan

We recently returned from our first visit to Japan. Karen and I have been wanting to go for quite a while, and the time was right – so most of the month of October was dedicated to that endeavor.

I loved our trip, and we were fortunate enough to even be in Kyoto during on of the festivals – Jidai Matsuri.

Our trip and tour included Kushiro, Tokyo, Nagoya, Hiroshima, Meijima Island, and Kyoto – as well as a number of places in between that will take a while to unblur in my memory.

Hiroshima Memorial

We took a tour through Samurai ToursBest of Japan, which I highly recommend if you want a good sampling of a wide swath of Japan. Their guides were excellent and informative, and I can’t thank Charlie enough for his instruction in how to navigate the signage for the Tokyo trains and subways, which more or less held us in stead through the entire trip. I do wish we could have stayed longer in some areas, but another trip in the future will have to do.

Yours truly, visiting a Studio Ghibli store in Kyoto
The Golden Shrine, in Kyoto
Looking around from the top of Miyajima Island, near Hiroshima

Tokyo subway map – yep, it’s complicated – but amazing!
Pigment, a dangerous store for artists…
giant buddha at Kamakura Daibatsu
The ryokan we stayed at in Takayama

The sheer artistry in every day life in Japan was amazing, and I miss it already being back in the US. Another trip in the future, I tell myself…

It is OK to test the framework

When I started to write the book Using Combine, I was learning the Combine framework as I went. There was a lot I was unsure about, and especially given that it was released with the beta of the operating system, the implementation was changing between beta releases as it firmed up. I chose to use a technique that I picked up years ago from Mike Clark – write unit tests against the framework to verify my understanding of it – while writing the book. (yes, I’m still working on it – it’s a very lengthy process)

While listening to a few episodes of the Under the Radar podcast, I heard a number of references to the idea of “make sure you’re not testing the framework”. It is generally good advice, in the vein of “make sure you’re testing your code first and foremost”, but as a snippet out of context and taken as a rule – I think it’s faulty. Don’t confuse what you are testing, but reliably testing underlying frameworks or libraries, especially while learning them or they evolve, can easily be worth the effort.

I have received a huge amount of value from testing frameworks – first in verifying that I understand what the library is doing and how it works. More over, it has been a very clear signal when regressions do happen, or intentional functionality changes.

If you do add tests of a framework or library into your codebase, I recommend you break them out into their own set of tests. If something does change in the library, it will be far more clear that it is a change from the library and not a cascading side effect in your code.

Most recently, this effort paid off when I stumbled across a regression in the Combine framework functionality with the GM release of Xcode 11.2. While I’ve been coming up to speed with the various operators, I’ve written unit tests that work the operators. In this case, the throttle operator – which has an option parameter latest – changed in how it operates with this release.

Throttle is very similar to the debounce operator, and in fact it operates the same if you use the option latest=true. They both take in values over time and return a single value for a specific time window. If you want the first value that’s sent within the timeframe, theoretically you should use latest=false with the throttle operator. This worked in earlier releases of Combine and Xcode – but in the latest release, it’s now disregarding that path and sending only the latest value.

You can see the tests I wrote to verify the functionality at, and right now I’m working on a pull request to merge in the change reflecting the current release and illustrating the regression. And before you ask, yes – I have submitted this as a bug to Apple (FB7424221). If you are relying on the specific functionality of throttle with latest=false, be aware that the latest release of Xcode & Combine is likely going to mess with it.

If you are more curious about all the other tests that were created to support Using Combine, then feel free to check out the github repository heckj/swiftui-notes – the tests are in the UsingCombineTests directory, and set up as they’re own test target in the Xcode project. There are more to write, as I drive down into the various operators, so I do expect more will appear. I won’t assert that they’re all amazing, well constructed tests – but they’re getting the job done in terms of helping me understand how they work – and how they don’t work.

Sharp Knives

After writing extensively with the Swift programming language, I recently spent time writing code in C++11. The experience has been very instructional, and I know have a much deeper appreciation for the guard rails that the language Swift has constructed. To my surprise, it has also left me with a renewed appreciation of the compiler tooling – LLVM, specifically the relative clarity of error messages.

C++ as a language was significantly more approachable to me after working on code using Swift for a while. There are a lot of parallels and similarities, which was particularly nice since I was porting code (re-writing the algorithms in another programming language). I think porting between programming languages is the rough equivalent of translating between human languages. In really comparing to allow you to move between the two, you become far more aware of the idiomatic conveniences and conventions.

One of the surprisingly pieces is my realization that I am far more attached to the swift concept of protocols than I had realized. C++ has a concept of interfaces, which is close – but definitely not the same in it’s breadth.

When combined with generic algorithms, the swift language feels far more capable and specific to me. In the swift programming language, you can constrain the implementation of your generic algorithms to only apply to specific protocols, which appears to be something you can’t easily do in C++ – or at least in C++11, which was the version I was working within. I found that programming with generics in C++ is far more reliant on convention, or possibly using subclasses – examples were a bit hard to come by for me.

My limited experience with C++ also leads me to think that the conventions followed between different groups of programmers is more diverse than Swift. The idiomatic patterns I found while reading other groups code had dramatically different patterns included within them. So much so that it was often hard to identify those patterns, and understand what was a team’s convention.

My time with the C++ components also makes me appreciate all the more the tendency of languages these days (to borrow from Python) to come “batteries included” with standard libraries. C++ standard library is more like tools to make tools, and some of the things commonly included with other languages (python, swift, etc) just have to be found individually and assembled.

While I have a bit more to do with C++ before I’ll be done with my project, I relish shifting back to the guard rails of swift. (I must admit, I’m now significantly more curious about the language Rust as well).

iPad Lost Mode

This past Saturday, I was on a 7am EDT flight from Orlando, FL to Seattle, WA – which means I was up at 3:30am east-coast-time to make the flight. That would be pretty harsh, except that my normal timezone is 4 hours later than that. The flight was smooth, and I half-slept most of the time. I took out my iPad and put it into the seat back pocket to work on it or read a bit during the flight, but never used it.

The following day after we were home, I went to get the iPad – and realized to my horror that I’d never pulled it from the seat-back pocket. The data was fortunately backed up, but loosing the hardware – a gift last Christmas – wasn’t a hit I wanted to take. We called the airlines baggage team, and they put in a lost report. I was pretty sure it was gone and resigned myself that I’d have to replace it some months down the road. I could simply make do until then, feeling foolish for leaving it in the seat pocket when I was half-asleep.

I logged into the Find my iPhone app on my iPhone, and marked the iPad in “lost mode”. I wanted it found, and had never used this feature previously. I set up the message that it was lost, and included my phone number – which shows on the lock screen. It hadn’t been able to connect to any networks where it already knew the wifi, so it was just “missing” from that system, but if and when it did connect – it would drop into “locked/lost” mode.

On Tuesday, the airlines called me and let me know they’d found an iPad matching my description. After a brief discussion, we verified that it was indeed mine. Within an hour I had several options for getting it back; choosing to have it delivered. I was expecting it to arrive “some time before 8pm on Wednesday”.

On Wednesday, I was at my usual coffee-house haunt, and saw a notification in email – “Your iPad has been found”! I checked the location, and it was my home address! Wait – the email notification was from 30 minutes ago.. So I called my sweetie and she ran downstairs and found… nothing!

She ran around the outside of the house three times, looking for any place where the box might have been left, but nothing. We immediately thought “OMG, it’s been stolen from our front porch” – as there’s a thing in our neighborhood where package theft is pretty common.

After looking again at the Find My Phone app, I realized that while it was “found” – it reported as being on the street in front of our house – and only for a minute, before disappearing again into the mists of who-knows-where. In hindsight, I imagine that the Fedex driver simply happened to be passing near our house at 9:17a. It was going slowly enough that the iPad was able to finally make a wifi connection it knew and register itself. Fedex, who was delivering it, reported that it was still undelivered, so after an hour or so of “theft panic”, that faded into a vague concern and hope that it really was still out for delivery. Fortunately updates from Fedex are nearly real-time, so if they’re reporting it is still in transit, there can be a reasonable amount of confidence that it is.

Over the course of the day, the Fedex delivery driver wandered around our neighborhood, delivering all their various packages. I got 2 more pings from the iPad, which also reported that it was “playing a noise” since it was lost. In both cases, it was near wifi networks that I’d previously connected with, and it was in those locations for only a minute or two. I can only imagine the driver being confused, if they heard the sound at all, coming from the back of their truck.

It was finally delivered home, around 6pm – nearly nine hours after first reporting itself in the area. It was in lost mode, and I was able to log in and recover it – everything intact. I felt extremely relieved, and even more that fortune had sided with me that day. Many friends have done or reported something similar, and devices forever disappear after that scenario.

I should mention that the Alaska Airlines team was fantastic through out this whole nerve-wracking scenario. They were super understanding when I called in panic, thorough about verifying the device was indeed mine when the found it, and efficient after getting the reports filed, made available online to me, and really flexible delivery options – including allowing me to come pick it up if I wanted.

The “lost device” feature was lovely, except when it wasn’t. It was like hearing distant calls for help that you can reach in time; sort of like the terrible dream where you can never make it to the end of the hallway to escape whatever dread it coming. I don’t know that any capability or feature of the iPad that would have made that better, it was just hellishly nerve-wracking to wait while it yelped in the back of that truck, wandering our my neighborhood.

A Using Combine update now available!

A new version of Using Combine (v0.7) is now available! 

The free HTML site of Using Combine has been updated automatically, and the PDF and ePub versions are available on Gumroad.

This version has relatively few updates, primarily focused on some of the missing publishers and resolving the some of the egregious flaws in ePub rendering. No significant changes have come with the later Xcode and IOS betas, and with Xcode 11 now in GM release, it was a good time for another update to be made available.

For the next release, I am focusing on fleshing out a number of the not-yet-written reference sections on operators, most of which are more specialized than the more generally used ones that have already been covered.

The project board at also reflects all the various updates still remaining to be written.

Using Combine (v0.6) available!

design by Michael Critz

A new version of Using Combine is available! The free/online version of Using Combine is updated automatically as I merge changes, and the PDF and ePub versions are released periodically and available on Gumroad. Purchase Using Combine

The book now has some amazing cover art, designed and provided by Michael Critz, and has benefited from updates provided by a number of people, now in the acknowledgements section.

The updates also include a section broken out focusing on developing with Combine, as well as a number of general improvements and corrections.

For the next release, I am going to focus on fleshing out a number of the not-yet-written reference sections:

the publishers I haven’t touched on yet

– starting into a number of the operators, most of which are more specialized

I reviewed the content prior to this release to see what was remaining to be done, and updated the project planning board with the various updates still remaining to be written.

I do expect we’ll see beta6 from Apple before too long, although exactly when is unknown. I thought it might appear last week, in which case I was planning on trying to accommodate any updates in this release. Xcode 11 beta6 hasn’t hit the streets and I wanted to get an update regardless of its inclusion.

navigating Swift Combine, tuples, and XCTest

What started out as a Github repository to poke at SwiftUI changed course a few weeks ago and became a documentation/book project on Combine, Apple’s provided framework for handling asynchronous event streams, not unlike ReactiveX. My latest writing project (available for free online at has been a foil for me to really dig into and learn Combine, how it works, how to use it, etc. Apple’s beta documentation is unfortunately highly minimal.

One of the ways I’ve been working out how its all operating is writing a copious amount of unit tests, more or less “poking the beast” of the code and seeing how it’s operating. This has been quite successful, and I’ve submitted what I suspect are a couple of bugs to Apple’s janky FeedbackAssistant along with tests illustrating the results. As I’m doing the writing, I’m generating sample code and examples, and then often writing tests to help illuminate my understanding of how various Combine operators are functioning.

In the writing, I’ve worked my way through the sections to where I’m tackling some of the operators that merge streams of data. CombineLatest is where I started, and it testing it highlighted some of the more awkward (to me) pieces of testing swift code.

The heart of the issue revolves around asserting equality with XCTest, Apple’s unit testing framework, and the side effect that Combine takes advantage of tuples as lightweight types in operators like CombineLatest. In the test I created to validate how it was operating, I collected the results of the data into an ordered list. The originated streams had simple, equatable types – one String, the other Int. The resulting collection, however, was a tuple of <(String, Int)>.

To use XCTAssertEquals, the underlying types that you are validating need to conform to Equatable protocol. In the case of checking a collection type, it drops down and relies on the equatable conformance of its underlying type. And that is where it breaks down – tuples in swift aren’t allowed to conform to protocols – so they can’t declare (or implement conformance with) equatable.

I’m certainly not the first to hit this issue – there’s a StackOverflow question from 2016 that highlights the issue, Michael Tsai highlights the same on his blog (also from 2016). A slightly later, but very useful StackOverflow Q&A entitled XCTest’ing a tuple was super helpful, with nearly identical advice to Paul Hudson’s fantastic swift tips in Hacking With Swift: how to compare equality on tuples. I don’t know that my solution is a good one – it really feels like a bit of a hack, but I’m at least confident that it’s correct.

The actual collection of results that I’m testing is based on Tristan’s Combine helper library: Entwine and EntwineTest. Entwine provides a virtual time scheduler, allowing me to validate the timing of results from operators as well as the values themselves. I ended up writing a one-off function in the test itself that did two things:

  • It leveraged an idea I saw in how to test equality of Errors (which is also a pain in the tuckus) – by converting them to Strings using debugDescription or localizedDescription. This let me take the tuple and consistently dump it into a string format, which was much easier to compare.
  • Secondarily, I also wrote the function so that the resulting tests were easy to read in how they described the timing and the results that were expected for a relatively complex operator like combineLatest.

If you’re hitting something similar and want to see how I tackled it, the code is public UsingCombineTests/MergingPipelineTests.swift. No promises that this is the best way to solve the problem, but it’s getting the job done:

func testSequenceMatch(
    sequenceItem: (VirtualTime, Signal<(String, Int), Never>),
    time: VirtualTime,
    inputvalues: (String, Int)) -> Bool {

    if sequenceItem.0 != time {
        return false
    if sequenceItem.1.debugDescription != Signal<(String, Int),
       Never>.input(inputvalues).debugDescription {
        return false
    return true

    testSequenceMatch(sequenceItem: outputSignals[0], 
                      time: 300, inputvalues: ("a", 1))

    testSequenceMatch(sequenceItem: outputSignals[1], 
                      time: 400, inputvalues: ("b", 1))

Tristan, the author of Entwine and EntwineTest, provided me with some great insight into how this could be improved in the future. The heart of it being that while swift tuples don’t/can’t have conformance to protocols like Hashable and Equatable, structs within Swift do. It’s probably not sane to make every possible combinatorial set in your code, but it’s perfectly reasonable to make an interim struct, map the tuples into it, and then use that struct to do the testing.

Tristan also pointed out that a different struct would be needed for the arity of the tuple – for example, a tuple of <String, Int> and <String, String, Int> would need different structs. The example implementation that Tristan showed:

struct Tuple2 {
  let t0: T0
  let t1: T1
  init(_ tuple: (T0, T1)) {
    self.t0 = tuple.0
    self.t1 = tuple.1
  var raw: (T0, T1) {
    (t0, t1)

extension Tuple2: Equatable where T0: Equatable, T1: Equatable {}
extension Tuple2: Hashable where T0: Hashable, T1: Hashable {}

A huge thank you to Tristan for taking the time to explain the tuple <-> struct game in swift!

After having spent quite a few years with dynamic languages, this feels like jumping through a lot of hoops to get the desired result, but I’m pleased that at least it also makes sense to me, so maybe I’m not entirely lost to the dynamic languages.

Writing with an AsciiDoc toolchain

I was about to start off with I’m not a technical writer by trade, but I realized that what I should be saying is “In addition to many other skills, I have done quite a bit of technical writing”. I have several published books and articles in my past, one book even still “in print”. I’ve written documentation for parts of many open source projects, countless internal corporate documents and created my own wiki structures, some of which weren’t even complete disasters. I’m still coming back to it again and again.

As it pertains to this post, I have written with ReStructuredText (and Sphinx to render), Hugo, Markdown and Jekyll. I had a strong preference for ReStructuredText for seriously-long-form writing (doc sites, books, etc) because it pretty sanely represented inter-document linkages, which always felt a like a terrible add-on hack and shim on Jekyll (w/ Markdown). Hugo, which Kubernetes docs uses was better – but the CLI tooling on the Mac was damned awkward. I do favor Hugo over Jekyll, especially for it’s internationalization support.

my writin’ toolchain creds…

When I did my last book project (Kubernetes for Developers), I ended up working with Packt Publishing. They have their own wonky internal toolchain setup, more or less a hacked-up version of WordPress from what I could tell. While I was working up the content, I seriously explored self-publishing. One of the ideas that I considered was looking more seriously at writing with AsciiDoc.

I’ve since taken a more serious stab at it, wanting to do some writing on Apple’s Combine framework. I decided I wanted to embrace the constraints of writing to a book format for this effort, and set up the content and toolchain to render HTML, PDF, and ePub concurrently. The core of the solution I landed on revolves around a lovely project called AsciiDoctor.

A caveat for folks reading this: If you’re wanting to do some online writing, and only want to render it to HTML, then while you can likely make this AsciiDoctor-based toolchain work, it’s honestly not the best tool for the job. You will probably be a lot happier with Jekyll or Hugo. AsciiDoctor & AsciiDoc are missing a lot of the “add on” flexibility and additional rendering pieces that are easily found in other HTML-specific rendering solutions (Jekyll, Hugo, and Sphinx).

The biggest constraint in my toolchain is the rendering to ePub. AsciiDoctor has a nice extension (asciidoctor-epub3), but it comes with some fairly strict structural constraints. If you want to adopt this toolchain for yourself, start with reading it’s composition rules.

The toolchain I use leverages prebuilt asciidoctor containers with Docker (so I don’t have to mess with ruby environments and maintaining that all together). The container (asciidoctor/docker-asciidoctor) is updated from the asciidoctor, and pretty easily usable. I did experiment with adding some extensions into my own docker image, but the baseline from the project is perfectly effective.

The key to using this setup is figuring out the correct invocation for the docker container so that the content runs on a local directory and generates the relevant output.

A sample of how I do this:

docker run --rm -v $(pwd):/documents/ --name asciidoc-to-html asciidoctor/docker-asciidoctor asciidoctor -v -t -D /documents/output -r ./docs/lib/google-analytics-docinfoprocessor.rb docs/using-combine-book.adoc
# copy the images directory over for the rendered HTML

cp -r docs/images output/images

docker run --rm -v $(pwd):/documents/ --name asciidoc-to-pdf asciidoctor/docker-asciidoctor asciidoctor-pdf -v -t -D /documents/output docs/using-combine-book.adoc

# ePUB

docker run --rm -v $(pwd):/documents/ --name asciidoc-to-epub3 asciidoctor/docker-asciidoctor asciidoctor-epub3 -v -t -D /documents/output docs/using-combine-book.adoc

I also wrote a simple bash script to make a one-line “re-render it all”, and tweaked it up so that it could also open the resulting file. If you’re so inclined, feel free to grab, copy, and use it yourself: re.bash

The example above, and my associated re.bash script, are set up to build content from a “docs” directory, with a specific “core” to the asciidoctor-based publication. In my case, I’ve called that file using-combine-book.adoc. My example embeds a Google Analytics code for the rendered HTML (omitting it for PDF and ePub of course), enables syntax-highlighting for source code blocks, and has the structure specifically enabled for ePub generation.

I’m hosting the content using Github Pages. At the time of this writing, they don’t support generating anything other than Jekyll with Markdown content through their built in system. You can, however, set up a TravisCI job to render the content (using the same docker containers) and then publish that by having the TravisCI job push the content to a specific gh-pages branch on the github repository.

Feel free to also snag and re-use the TravisCI configuration (.travis.yml). You’ll need to add 3 environment variables to your Travis job to make this work:


The last of these is a “personal access token”, which is what allows the travis job to push content to your repository as you. Do make sure you tweak the repository name and location to match your own if you copy this. It’s worth mentioning that I extended the basic example I found at, and the .travis.yml file I linked will only push updates when they’re merged with the master branch on the repository.

The end result is effective and I’m happy with the toolchain

It doesn’t come without it’s own constraints, primarily imposed by my desire to create an ePub format at the end of this process. I’ve also been happy with the effectiveness of AsciiDoc, although frankly I’m still just learning the basics. If you’re curious about the markup language itself, I’ve found the AsciiDoc Syntax Quick Reference and Asciidoctor User Manual to be invaluable references. I keep a tab open to each of those pages for reference while I’m writing.

If you’re so inclined to view the current work-in-progress, you can see the rendered HTML content at, which is derived from the asciidoc content within I also go ahead and publish the PDF and ePub in the same fashion, available at and respectfully.