Function: __
Help: __: integral concatenation of strings.
Section: symbolic_operators
Description:
 (genstr, genstr):genstr                gconcat($1, $2)
 (genstr, gen):genstr                   gconcat($1, $2)
 (gen, genstr):genstr                   gconcat($1, $2)
 (gen, gen):genstr                      gconcat($genstr:1, $2)
