First answers

solution.pl

@@ -3,13 +3,13 @@
 Prints the names of all existing tables, one per line (use writeln/1).
 A table name is always an atom.
 */
-tables.
+tables :- tabl(X, _), writeln(X).
 
 :- dynamic tables/1.
 /*
 Unify Tables with a list of the names of all existing tables.
 */
-tables(Tables).
+tables(Tables) :- findall(X, tabl(X, _), Tables).
 
 :- dynamic create_table/2.
 /*
@@ -20,7 +20,9 @@ If a table with the given name already exists, the predicate must throw a
 descriptive exception (use throw/1).
 All exceptions must have a descriptive error message.
 */
-create_table(Table, Cols).
+create_table(Table, Cols) :-
+	(tabl(Table, _) -> throw("Table already exists"));
+		assertz(tabl(Table, Cols)).
 
 :- dynamic cols/2.
 /*
@@ -186,4 +188,4 @@ query(Query, Result).
 /*
 cf. query/2
 */
-query(Query).
+query(Query).