unknown_warning.m:017: Warning: the first element of the list following the
unknown_warning.m:017:   `disable_warning' keyword, `singleton_varx', is not
unknown_warning.m:017:   the name of a warning, so the compiler cannot act on
unknown_warning.m:017:   it.
unknown_warning.m:020: In clause for predicate `unknown_warning'/3:
unknown_warning.m:020:   warning: variable `D' occurs only once in this scope.