Concatenate two shears. The result is NOT a shear, but must be represented by a generalized 2x2 transform. Defer the implementation until we can declare a 2x2 matrix. [1 YYA] * [1 YYB] == [1+YYA*XXB YYB*YYA] [XXA 1] [XXB 1] [XXA+XXB XXA*XXB+1]