Proved zadd_left_commute and zmult_left_commute to define
zadd_ac and zmult_ac. Deleted add_cong, add_kill and add_left_commute_kill as
unused. Defined zadd_simps, zminus_simps, zmult_simps and added them to
integ_ss.
#! /bin/csh
grep "$*" {Pure/Syntax,Pure/Thy}/*ML */*ML */*/*ML