Write a function named is_chessboard_square that accepts a single string argument and returns whether that string is the name of a valid chessboard square. Chessboard squares are exactly two characters long: first a lowercase letter between a and h, then a number between 1 and 8. For example, "e4" is a valid square, but "i1" (invalid letter) and "f9" (too large number) are not.

You may find it helpful to use the < and > operators to compare strings.