cols function

solution.pl

@@ -31,7 +31,9 @@ order as they were supplied to create table/2).
 If the given table does not exist, the predicate must throw a descriptive
 exception (use throw/1).
 */
-/* cols(Table, Cols). */
+cols(Table, Cols) :-
+	(tabl(Table, _) -> tabl(Table, Cols));
+		throw("Table doesn't exist").
 
 :- dynamic row/2.
 /*