Handle expressions not representable by SymPy

mathics/builtin/numbers/algebra.py

@@ -402,8 +402,9 @@ def eval(self, expr, var, evaluation: Evaluation):
 
         expr_sympy = expr.to_sympy()
         var_sympy = var.to_sympy()
+        # If the expression cannot be handled by Sympy, just return it.
         if expr_sympy is None or var_sympy is None:
-            return None
+            return expr
 
         try:
             result = sympy.apart(expr_sympy, var_sympy)
@@ -1393,8 +1394,9 @@ def eval(self, expr, evaluation):
         "Factor[expr_]"
 
         expr_sympy = expr.to_sympy()
+        # If the expression cannot be handled by Sympy, just return it.
         if expr_sympy is None:
-            return None
+            return expr
 
         try:
             return from_sympy(sympy_factor(expr_sympy))

mathics/eval/numbers/numbers.py

@@ -207,8 +207,9 @@ def cancel(expr):
     else:
         try:
             result = expr.to_sympy()
+            # If the expression cannot be handled by Sympy, just return it.
             if result is None:
-                return None
+                return expr
 
             # result = sympy.powsimp(result, deep=True)
             result = tracing.run_sympy(sympy.cancel, result)