lo.logic – Applications of Zorn’s lemma that aren’t chain-complete/directed-complete?

Zorn’s Lemma applies to posets in which every chain has an upper bound. However, in all applications I know, the poset is also evidently chain-complete — chains have least upper bounds. A few classic such applications:

  • AC, using a poset of “partial choice functions”
  • the Well-Ordering Principle, using a poset of “partial well-orderings” (ordered by end-extension, not simply $subseteq$)
  • Hahn–Banach, using a poset of “partial functionals defined on subspaces”
  • extension of filters to ultrafilters, using a poset of filters.

Are there any natural applications of Zorn’s Lemma where the poset isn’t chain-complete, or where chain-completeness is less obvious than existence of upper bounds?

(Indeed, all examples I know are equally obviously directed-complete. Under AC, this is equivalent to chain-complete, but constructively, directed-completeness is stronger. For those wondering why I’m caring about use of AC while considering Zorn’s Lemma, note that constructively, ZL does not imply AC — this is shown in John Bell’s very nice analysis Zorn’s lemma and complete Boolean algebras in intuitionistic type theories, JSL 1997, https://doi.org/10.2307/2275642. His surprising (to me) insight is that ZL itself doesn’t imply LEM or AC — most applications, including the classical proof of ZL=>AC, use LEM for the final step “a maximal partial object must be total”.)

rhythmbox – Music apps aren’t recognizing/syncing with my iFuse-mounted iPhone

So close to getting music syncing with the iPhone working, but still – so far! I can plug my iPhone into my machine* and mount it using iFuse. I can find the music files on my iPhone and pull them off, despite the tremendously weird file stuff iTunes did to them. But Rhythmbox and Clementine don’t recognize my iPhone as a device, so I can’t get files back onto the phone in a way Music on the phone recognizes. I could use VLC mobile but I’m partial to CS Music which pulls the file library from the Music database. Is there a way to get one of these apps to recognize the iTunes database on the phone? Thanks!

Mark

  • elementary OS 5.1.7 with 5.9.0-050900

Will PostgreSQL use parts of a composite index even if all parts aren’t listed in the where clauses?

Yes, because that composite index in your example is also known as a covering index. Specifically mentioned in the previously linked documentation here:

…people sometimes made covering indexes by writing the payload columns as ordinary index columns, that is writing
CREATE INDEX tab_x_y ON tab(x, y);
even though they had no intention of ever using y as part of a WHERE clause. This works fine as long as the extra columns are trailing columns…

Basically, as long as the fields of your predicates are all sequentially part of the index definition (from left to right), then that index is covering and applicable to be used for that query.

The reverse of your example would not work though since the index does not cover that scenario. I.e. WHERE colB = 'someValue' is not covered by an index with the definition of (colA, colB) since the order of the field list in the index definition literally defines the structure of the underlying B-Tree used to sort the data. So first the data is sorted on colA and then colB, making it not possible to directly search on colB without a predicate to search on colA first.

c# – Why aren’t my conditional compilation symbols working when I dotnet publish my .NET Core 3 project?

I have a project which is targeting .NET Core 3. This project builds and runs fine in both Debug and Release configurations. Both configurations have a Conditional compilation symbol set in Visual Studio of Glue.

enter image description here

The resulting .csproj has the following:

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x86'">
  <DefineConstants>TRACE;GLUE</DefineConstants>
  <OutputPath></OutputPath>
</PropertyGroup>

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x86'">
  <DefineConstants>TRACE;GLUE</DefineConstants>
</PropertyGroup>

As I mentioned earlier, if I run through Visual Studio, all works fine.

If I publish my app through the command line interface, the resulting app seems to ignore the conditional compilation symbol.

As a test, I added an #if around a section of code which will cause compile errors if the #if is excluded.

#if GLUE
        public MainGlueWindow()
        {
#endif
            mSelf = this;

            ...

If the GLUE conditional compilation symbol is considered, the code should compile fine, but I do get errors when I perform a dotnet publish. The full command I am using is:

dotnet publish GlueFormsCore.csproj -r win-x86 -c Debug

The error suggests the constructor header is missing:

C:UsersvchelDocumentsGitHubFlatRedBallFRBDKGlueGlueMainGlueWindow.cs(95,19): error CS1519: Invalid token '=' in class, record, struct, or interface member declaration (C:UsersvchelDocumentsGitHubFlatRedBallFRBDKGlueGlueGlueFormsCore_tksugttl_wpftmp.csproj)

I should point out that x86 is the only platform in my csproj.

I don’t know if the problem is caused by the absence of specifying x86 as the platform, but if so I don’t know how to specify that on the dotnet publish command.

Can anyone tell me why the dotnet publish command is not considering the GLUE conditional compilation symbol?

9 – Why aren’t the already installed modules recognized?

I want to migrate my Drupal 7 site to Drupal 9. I test that with my DEV site to see how far I will come, but right at the beginning, when I start the upgrade, I get to the /upgrade/review page.

screenshot

It tells me that I have to install some modules in Drupal 9 first to get the configuration from my old site. I downloaded and installed and activated some of these 96 missing modules into my new blank Drupal 9 site, but the list doesn’t change. It doesn’t recognize the modules already installed in Drupal 9.

What am I missing?

ssl – Why aren’t my websites configured in IIS using the correct certificates?

My sites are similarly named:

  • hi.api.domain.tld
  • hi.test.domain.tld

The .api domain is my api and .test is the webapp that consumes the api.

I’ve got a certificate for each one but they don’t seem to be working right.

One of them works fine:

Certificate Name matches hi.test.
Subject hi.test.redacted

The other one, however, seems to be using this same certificate (hi.test) for the hi.api site according to digicert:

Certificate does not match name hi.api.
Subject hi.test.redacted

The reason why is a mystery to me because the certificate I’ve configured for use on the hi.api site is, in fact, the one for hi.api (see image below).

I’m really not a server guy so I can’t even guess at the cause or how to fix. I’m not even sure what to google to find an answer here so if anyone has any insight or can point me in the right direction, I’d really appreciate it.

Thanks in advance.

enter image description here

standards – Why are there not more interactive design / style guides out there? Aren’t they more user friendly?

As Devin says in his comment, this question will get answers based on personal opinions and observations. These are mine.

In my experience there is a difference between a brand guidelines(like Uber’s) and overall design guidelines. There are a lot of public brand guidelines out there and most of them to allow third parties to use their brand and while doing so they should do it the right way.

Overall design guidelines or product design guidelines is another thing. The questions answer by those is how the general look and feel of a product in a specific environment or ecosystem should be.

A great example of “complete” design guidelines is Atlassian’s. It consists of three main features; product design, brand and user interface. It’s used by their own teams for developing new features and products but also to help the plugin developers to build their plugin with the “Atlassian look and feel”. This will help the end user transition between an official Atlassian product and a third party plugin.

The same arguments could be applied to Apple’s iOS guidelines or Google’s material design guidelines. They all want the transitions to be as gentle as possible and keep an unified feel of the ecosystem.

A thing to remember though, these guidelines should not restrain a developer or a designer – they should help and be looked as what they are, guidelines.

numerical analysis – Why aren’t Grobner bases more common?

I have only heard of / seen Grobner bases in passing, but my understanding is that they are much like vector bases but for polynomials instead of linear systems. I know polynomials are used in CAD and graphics at the very least. Is there any particular reason why I haven’t seen Grobner bases in application? I’m trying to determine whether they are worth the time to learn for my own work.