# The sheep and the wolves

When I was a child, I was playing a game such as the following:

• The game is played on a standard chessboard, but only on the black squares.
• There are two players: the white player has a single white pawn which is the "sheep"; the black player has four pawns which are the "wolves".
• The players start at opposite sides of the board, and make a single diagonal step each turn.
• The goal of the wolves is to capture the sheep - surround it such that it cannot move.
• The goal of the sheep is to escape the wolves and get to the opposite side of the board.

Recently I tried playing it again, but found out that I do not remember the exact rules. Specifically: * Is the sheep allowed to go backward, or only forward? * Are the wolves allowed to go backward, or only forward?

We tried to play this game with all four combinations. In each combination, the game turned out to be too easy for one side and too difficult for the other side.

What are the rules that make this game sufficiently challenging for both sides?