prolog-electric-underscore-flag

prolog-electric-underscore-flag is a variable defined in `prolog.el'.
Its value is

nil

Documentation:
Non-nil means make underscore key electric.
Electric underscore replaces the current variable with underscore.
If underscore is pressed not on a variable then it behaves as usual.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.