Lame, but I wrote Prolog that year. I read about it on some magazine and there was no mention of the cut. So I invented new definition symbol ":=". Under that r

Lame, but I wrote Prolog that year. I read about it on some magazine and there was no mention of the cut. So I invented new definition symbol ":=". Under that rule there is no backtrack. It looked actually better and was more comprehensible than "!".