rem: return scheme_apply(argv[0], 1, NULL);
add: return scheme_apply(argv[0], 0, NULL);
context: call_with_continuation_barrier (int argc, Scheme_Object *argv[]){  scheme_check_proc_arity("call-with-continuation-barrier", 1,			  0, argc, argv);  return scheme_apply(argv[0], 1, NULL);}