\colon for maps in opposite direction

Question

Using \colon gives correct spacing for a map $F\colon C\to D$ in one direction. But writing $L\colon C\rightleftarrows D\colon R$ for a couple of maps in both directions (e.g. for an adjunction) gives disturbingly asymmetric spaces near first and second colons (like if D were a map from R, not the other way round). Probably, it should be fixed (e.g. some other command should be used) — but how?

Answer 1

amsmath defines \colon as \nobreak \muskip 2mu\mathpunct{}\nonscript\mkern-\thinmuskip{:}\mskip 6mu plus1mu\relax. So how about the following?

\newcommand*\cocolon{%
        \nobreak
        \mskip6mu plus1mu
        \mathpunct{}%
        \nonscript
        \mkern-\thinmuskip
        {:}%
        \mskip2mu
        \relax
}