Pure/drule/cprems_of, cskip_flexpairs, cstrip_imp_prems: new cterm operations
Pure/drule/cprems_of, cskip_flexpairs, cstrip_imp_prems: new cterm operations

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle