This predicate only succeeds for a PredSpec which is known to be a built-in. Undefined Predspec's raise an exception.
Success: is_built_in(nl/0). is_built_in(write/1). Fail: is_built_in(append/3). % append/3 is a library % predicate, not a built-in. Error: is_built_in(X). (Error 4). is_built_in(a/X). (Error 4). is_built_in(a). (Error 5). is_built_in(1). (Error 5). is_built_in(undefined/0). (Error 60).