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When displaying the intersection symbol in equations, e.g.,

$$Hom(A,B) \cap Hom(B,C)$$

I find that the "cap" is too small; its height is, in fact, subordinate to the surrounding content. On the other hand, \bigcap is entirely too big, dwarfing the surrounding content. This is especially unnecessary if the intersection is not indexed, for example. What is needed is a "medium" cap whose size is somewhere between the big cap and the regular cap. Does such a symbol/construct exist?

Note that similar comments apply to \bigcup and \cup.

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1  
You should use \[ ... \] for display math instead of SS ... SS as per Why is [ … ] preferable to $$? –  Peter Grill Dec 18 '11 at 19:08
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I've found that the size of \bigcap changes depending on whether you are inside $'s or $$'s. It is smaller when you force it to be in-line with $'s. –  jamaicanworm Dec 18 '11 at 19:22
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Also, if you're writing text within math, use \text{<text>} from the amsmath package. If Hom is an operator (like \sin), use \DeclareMathOperator{\Hom}{Hom} and use \Hom(A,B), or on-the-fly \operatorname{Hom}(A,B), say. Both of the last commands are supplied by amsopn (which is included when you load amsmath). –  Werner Dec 18 '11 at 19:28
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@jamaicanworm: This depends on the math mode you're in, apparently. \bigcap (and others) fall under the scope of "Variable-sized Math Operators" (see Table 57 on p 25 of The Comprehensive LaTeX Symbol List). –  Werner Dec 18 '11 at 19:47

2 Answers 2

up vote 8 down vote accepted

You can use scalebox from the graphicx package to create one:

enter image description here

\documentclass{article}
\usepackage{graphicx}

\newcommand*{\medcap}{\mathbin{\scalebox{1.5}{\ensuremath{\cap}}}}%
\begin{document}
\[ Hom(A,B) \cap    Hom(B,C)\]
\[ Hom(A,B) \medcap Hom(B,C)\]
\[ Hom(A,B) \bigcap Hom(B,C)\]
\end{document}
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I don't find it to be too small. You can use the same symbol as \bigcap, but not in the "bigger" version, so there's some work to do:

\newcommand*\mcap{\mathbin{\mathpalette\mcapinn\relax}}
\newcommand*\mcapinn[2]{\vcenter{\hbox{$\mathsurround=0pt
  \ifx\displaystyle#1\textstyle\else#1\fi\bigcap$}}}

This is the result of

\[\operatorname{Hom}(A,B)\cap\operatorname{Hom}(B,C)\]

and of

\[\operatorname{Hom}(A,B)\mcap\operatorname{Hom}(B,C)\]

You need \usepackage{amsmath} to use \operatorname and you might want to say

\DeclareMathOperator{\Hom}{Hom}

in the preamble, in order to be able to use \Hom as an abbreviation.

enter image description here

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