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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeApr 26th 2016
   • (edited Apr 26th 2016)
   • PermaLink
   Author: Urs
   Format: MarkdownItexIn the following diagram (and in many more that float around on the nLab), on my system the lower arrow is too short: $$ Top_{cg}^{\ast/} \stackrel{\overset{X \wedge (-)}{\longleftarrow}}{\underset{Maps(X,-)_\ast}{\longrightarrow}} Top_{cg}^{\ast/} $$ $$ Top_{cg}^{\ast/} \stackrel{ \overset{X \wedge (-)}{\longleftarrow} }{ \underset{Maps(X,-)_\ast}{\longrightarrow} } Top_{cg}^{\ast/} $$ This didn't use to be this way. Any ideas?

   In the following diagram (and in many more that float around on the nLab), on my system the lower arrow is too short:

   $$Top_{cg}^{\ast/} \stackrel{\overset{X \wedge (-)}{\longleftarrow}}{\underset{Maps(X,-)_\ast}{\longrightarrow}} Top_{cg}^{\ast/}$$

     $$
       Top_{cg}^{\ast/}
          \stackrel{
            \overset{X \wedge (-)}{\longleftarrow}
          }{
            \underset{Maps(X,-)_\ast}{\longrightarrow}
          }
       Top_{cg}^{\ast/}
     $$
   

   This didn’t use to be this way.

   Any ideas?

2. • CommentRowNumber2.
   • CommentAuthorMike Shulman
   • CommentTimeApr 26th 2016
   • PermaLink
   Author: Mike Shulman
   Format: MarkdownItexSame here. But what I don't understand is why the top arrow lengthens; the bottom one that doesn't lengthen is what I would expect. In standard TeX, at least, `\longrightarrow` has a fixed length and you need something like `\xrightarrow` if you want it to stretch.

   Same here. But what I don’t understand is why the top arrow lengthens; the bottom one that doesn’t lengthen is what I would expect. In standard TeX, at least, \longrightarrow has a fixed length and you need something like \xrightarrow if you want it to stretch.

3. • CommentRowNumber3.
   • CommentAuthorTodd_Trimble
   • CommentTimeApr 26th 2016
   • PermaLink
   Author: Todd_Trimble
   Format: MarkdownItexIn this old [iTeX document](https://golem.ph.utexas.edu/~distler/blog/itex2MMLcommands.html) it explains that all arrows in iTeX are supposed to be stretchy. So this may be a bug.

   In this old iTeX document it explains that all arrows in iTeX are supposed to be stretchy. So this may be a bug.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeApr 28th 2016
   • (edited Apr 28th 2016)
   • PermaLink
   Author: Urs
   Format: MarkdownItexSome more experimenting: If in the above example I replace the \stackrel{top}{bottom} with a \underoverset{bottom}{top}{} (the last argument empty) then I get $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {} Top_{cg}^{\ast/} $$ $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {} Top_{cg}^{\ast/} $$ At least on my system, now neither of the two arrows stretches, both are as short as the one in the previous example that looked too short. But now look what happens as I add in a third arrow in between: $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\overset{abcdefghijkl}{\longrightarrow}} Top_{cg}^{\ast/} $$ $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\overset{abcdefghijkl}{\longrightarrow}} Top_{cg}^{\ast/} $$ At least on my system, now the top and bottom arrows are both nicely long as they should be. Now the middle arrow is too short. I would understand if somebody decided that the arrows in subscripts and superscripts should not be strechy, while only those on the main line should. But in this last example the behaviour is the opposite of that, while in the previous one it is both or neither. Probably this needs to be reported as a bug somewhere.

   Some more experimenting:

   If in the above example I replace the

     \stackrel{top}{bottom}
   

   with a

     \underoverset{bottom}{top}{}
   

   (the last argument empty) then I get

   $$Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {} Top_{cg}^{\ast/}$$

       $$
         Top_{cg}^{\ast/}
            \underoverset
            {
              \underset{Maps(X,-)_\ast}{\longrightarrow}
            }
            {
              \overset{X \wedge (-)}{\longleftarrow}
            }
            {}
         Top_{cg}^{\ast/}
       $$
   

   At least on my system, now neither of the two arrows stretches, both are as short as the one in the previous example that looked too short.

   But now look what happens as I add in a third arrow in between:

   $$Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\overset{abcdefghijkl}{\longrightarrow}} Top_{cg}^{\ast/}$$

       $$
         Top_{cg}^{\ast/}
            \underoverset
            {
              \underset{Maps(X,-)_\ast}{\longrightarrow}
            }
            {
              \overset{X \wedge (-)}{\longleftarrow}
            }
            {\overset{abcdefghijkl}{\longrightarrow}}
         Top_{cg}^{\ast/}
       $$
   

   At least on my system, now the top and bottom arrows are both nicely long as they should be. Now the middle arrow is too short.

   I would understand if somebody decided that the arrows in subscripts and superscripts should not be strechy, while only those on the main line should. But in this last example the behaviour is the opposite of that, while in the previous one it is both or neither.

   Probably this needs to be reported as a bug somewhere.

5. • CommentRowNumber5.
   • CommentAuthorMike Shulman
   • CommentTimeApr 28th 2016
   • PermaLink
   Author: Mike Shulman
   Format: MarkdownItexI also see what you see. I suppose a place to start debugging, or at least figuring out who to report the bug to, is to check out the MathML that's being generated. Does MathML have a "stretchy" attribute that's just missing on some of the arrows generated by iTeX? Or do all the arrows look the same in the MathML and they're just being displayed wrong by the browser?

   I also see what you see.

   I suppose a place to start debugging, or at least figuring out who to report the bug to, is to check out the MathML that’s being generated. Does MathML have a “stretchy” attribute that’s just missing on some of the arrows generated by iTeX? Or do all the arrows look the same in the MathML and they’re just being displayed wrong by the browser?

6. • CommentRowNumber6.
   • CommentAuthorDavidRoberts
   • CommentTimeApr 28th 2016
   • PermaLink
   Author: DavidRoberts
   Format: MarkdownItexCan you put a phantom arrow in between? It's a hack, I know...

   Can you put a phantom arrow in between? It’s a hack, I know…

7. • CommentRowNumber7.
   • CommentAuthorUrs
   • CommentTimeApr 29th 2016
   • (edited Apr 29th 2016)
   • PermaLink
   Author: Urs
   Format: MarkdownItexOh,I didn't know that \phantom works here! Thanks for the suggestion. Yes, that does the trick $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\phantom{\longrightarrow}} Top_{cg}^{\ast/} $$ $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\phantom{\longrightarrow}} Top_{cg}^{\ast/} $$ Incidentally, the width of a \, is insufficient, but the width of a \bot is sufficient to trigger the behaviour: $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\bot} Top_{cg}^{\ast/} $$ $$ Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\bot} Top_{cg}^{\ast/} $$ This is a nice way to typeset adjunctions.

   Oh,I didn’t know that \phantom works here! Thanks for the suggestion. Yes, that does the trick

   $$Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\phantom{\longrightarrow}} Top_{cg}^{\ast/}$$

        $$
           Top_{cg}^{\ast/}
              \underoverset
              {
                \underset{Maps(X,-)_\ast}{\longrightarrow}
              }
              {
                \overset{X \wedge (-)}{\longleftarrow}
              }
              {\phantom{\longrightarrow}}
           Top_{cg}^{\ast/}
         $$
   

   Incidentally, the width of a

     \,
   

   is insufficient, but the width of a

     \bot
   

   is sufficient to trigger the behaviour:

   $$Top_{cg}^{\ast/} \underoverset { \underset{Maps(X,-)_\ast}{\longrightarrow} } { \overset{X \wedge (-)}{\longleftarrow} } {\bot} Top_{cg}^{\ast/}$$

         $$
           Top_{cg}^{\ast/}
              \underoverset
              {
                \underset{Maps(X,-)_\ast}{\longrightarrow}
              }
              {
                \overset{X \wedge (-)}{\longleftarrow}
              }
              {\bot}
           Top_{cg}^{\ast/}
         $$
   

   This is a nice way to typeset adjunctions.