prettify-symbols-mode to handle "\alpha-\beta" ...

[pietru]

I am using prettify-symbols-mode for displaying greek command using
the corresponding greek glyph when using mathematical expressions
in texinfo.

Here is an example

  (push '("\\alpha" . ?α) prettify-symbols-alist)
  (push '("\\beta" . ?β) prettify-symbols-alist)

This works well when using "\alpha\beta", "\alpha - \beta" 
But the expression fails when using "\alpha-\beta" or
"\alpha_i", "\alpha_{ij}", "\beta^i", "\beta+\alpha".
The expressions are all valid mathematical expressions
when using tex.  

Would you be so kind to update "prettify-symbols-mode"
so the substitutions can become possible to handle.

Does this require that SYMBOL in (SYMBOL . CHARACTER) be
a regexp?

Regards
Pietru