* juan mari alberdi (2007-01-23) writes:
The following one, however, doesn't,
'... If you enter a dollar sign that matches a double dollar sign `$$'
AUCTeX will
automatically insert two dollar signs. If you enter a second dollar
sign that matches a single dollar sign, the single dollar sign will
automatically be converted to a double dollar sign...'
That behavior was disabled because double dollar insertion and removal
was asymmetric and because we don't want to encourage people inserting
double dollar signs in LaTeX files. It can screw up spacing in the
typeset document. Use \[...\] or displaymath environments instead.
You can reactivate the old behavior by customizing
`TeX-math-close-double-dollar'. I'll update documentation to reflect
that.