
I would like you to implement a module named TopModule with the following
interface. All input and output ports are one bit unless otherwise
specified.

 - input  p1a
 - input  p1b
 - input  p1c
 - input  p1d
 - input  p2a
 - input  p2b
 - input  p2c
 - input  p2d
 - output p1y
 - output p2y

The 7400-series integrated circuits are a series of digital chips with a
few gates each. The 7420 is a chip with two 4-input NAND gates. The
module should implement the same functionality as the 7420 chip.

