multiply variable by itself instead of using power function

firstpass_learner.py

@@ -22,7 +22,7 @@ def l1_norm(*exprs) -> z3.ExprRef:
     return z3.Sum(*(abs_expr(expr) for expr in exprs))
 
 def l2_norm(*exprs) -> z3.ExprRef:
-    return z3.Sum(*(expr**2 for expr in exprs))
+    return z3.Sum(*(expr*expr for expr in exprs))
 
 def max_expr(*exprs) -> z3.ExprRef:
     m = exprs[0]
@@ -99,7 +99,7 @@ class FirstpassLearner(Z3LearnerBase):
             print("(unsat)")
             return None
         else:
-            print("(unknown)")
+            print("(unknown) or timeout!")
             return None