M

Just added a `fact(x)` function using `math.factorial`. Added it on my machine, figured it wouldn't hurt to add here, too.

Support for factorial n!

4

**Is your feature request related to a problem? Please describe.** No. **Describe the solution you'd like** ```csharp var expression = new Expression("5!"); Debug.Assert(120 == expression.Evaluate()); ``` **Describe alternatives you've considered**...