Solution

The game of chess has a well-defined set of rules according to which it can be played. Furthermore, these rules can be correctly interpreted by a computer. However, these rules only say how to form a valid move, but not which move to choose. In other words, the rules of chess do not supply a computer with the sequence of operations to follow in order to interpret them. Rather, they restrict the choice to a subset of all possible sequences of operations (moves) to perform. In this sense, the rules of chess do not form valid instructions. Therefore, they are not a programming language. Computers programs that play chess only use the rules of chess as a constraint on the possible moves, but they use much more complex algorithms to determine which move to make.