> I guess, the point was, if list is a built-in construct, the function length should be also built in. It is built in. No need to write your own length predic

> I guess, the point was, if list is a built-in construct, the function length should be also built in. It is built in. No need to write your own length predicate. The quoted example is an illustration of a possible implementation. (Cue boring discussion of "built in" vs. "defined in the standard library".)