Musings

Consider the following commutative diagram.

$$\begin{matrix} B^{\mathrlap{A}} & \longrightarrow & 1^{\mathrlap{A}} \\ \mathllap{\scriptsize{\sigma^A}}\downarrow & & \downarrow\mathrlap{\scriptsize{t^\alpha}} \\ P(B)^{\mathrlap{A}} & \underset{\chi_\sigma^A}{\longrightarrow} & P(1)^{\mathrlap{A}} \end{matrix}$$

To get the vertical arrows to line up correctly, I used the aforementioned \mathrlap{} and \mathllap{} commands:

 \begin{matrix}
  B^{\mathrlap{A}} & \longrightarrow & 1^{\mathrlap{A}} \\
  \mathllap{\scriptsize{\sigma^A}}\downarrow & & \downarrow\mathrlap{\scriptsize{t^\alpha}} \\
  P(B)^{\mathrlap{A}} & \underset{\chi_\sigma^A}{\longrightarrow} & P(1)^{\mathrlap{A}}
 \end{matrix}

(Previously my best attempt, at getting this right, involved games with the aligned environment. This is simpler and better.)

How about \mathclap{}? Look at all the whitespace in $$X = \sum_{1\le i\le j\le n} X_{ij}$$

It’s nicer to collapse that whitespace, using

  X = \sum_{\mathclap{1\le i\le j\le n}} X_{ij}

which produces $$X = \sum_{\mathclap{1\le i\le j\le n}} X_{ij}$$

Anyway, this is all — as you can see — implemented in itex2MML 1.3.13. And, of course, Instiki’s LaTeX export includes the needed macro definitions.

I’m eager for MathML3, which will allow the obvious vertical generalizations, \mathulap{} and \mathdlap{}, to be defined.