Let f(x3, x2, x1, x0) = (y1, y0) such that y1 = 1 if the number of 1s in x3x2x1x0 is even, 0 otherwise, and, output y0 = 1 if the number of 1s in x3x2x1x0 is odd, 0 otherwise.

1. (20 points) Implement f with four 2-to-4 decoders.

2. (20 points) Implement f with a 4-to-1 multiplexer with selection inputs x0, x1 (in this order).