This is white's turn. The player moves his pawn.
The pawn's previous and current positions are given.
Determine whether the move was valid.
pawn's previous pos = 'b2' pawn's previous pos = 'c3'
So this is a valid move provided there was an opponent piece on c3.
But for now, just check the validity of the move. Opponent's pieces will be added in the next problem.