Scm_SysSigsetOp  2578 src/gauche.h   SCM_EXTERN ScmObj Scm_SysSigsetOp(ScmSysSigset*, ScmObj, int);
Scm_SysSigsetOp   873 src/syslib.c    SCM_RESULT = (Scm_SysSigsetOp(set, sigs, FALSE));
Scm_SysSigsetOp   898 src/syslib.c    SCM_RESULT = (Scm_SysSigsetOp(set, sigs, TRUE));