challenge 20 not correct

[sgerodes]

// Should NOT
exd5(ep) // En passant could end only on the 6th and 3rd ranks
exd2(ep)

//Should
Rdxd2
Rexe2
R2xe2

Could also add this:
//SHOULD
Ba1b2 // Is possible, if a promotion to Bishop were done (e.g. Bishops are on a1 and h8), so there are two same-colored bishops

// NOT
Rd1e2 // if you want to do the challenge hard. Because the Rock cant change both coordinates at ones
Ba1b1 // also probably hard to regex, but this notation is not possible. The bishop cant change colors