Potential typo in Cos

In `Cos.CosProc()`  should

```
if (n == 2)
{
    if (Mod(k, 2) == 1) return 0;
}
```

be

```
if (n == 2)
{
    if (Mod(k, 4) == 1) return 0;
}
```

?

This would match the pattern of modding by n*2 and the Sin.SinProc() method.
