-- CSI2111 Assignment-2 Q1(b)
-- Implementation of f(w,x,y,z) = (x+z')(w+y+z') using NOR gates.
-- Simplified expression is f(w,x,y,z) = ((x + z')' + ((w + y)'' + z')')' 

LIBRARY ieee;
USE ieee.std_logic_1164.all;

ENTITY a2q1b IS
	PORT ( w, x, y, z  : IN  STD_LOGIC;
		   f		   : OUT STD_LOGIC);
END a2q1b;

ARCHITECTURE nor_only OF a2q1b IS
SIGNAL s1,s2 : STD_LOGIC;
BEGIN
    s1 <= z NOR z;				-- assign z' to temporary signal s1
    s2 <= w NOR y;				-- assign (w+y)' to temporary signal s2
	F <=  (x NOR s1) NOR ((s2 NOR s2) NOR s1);
END nor_only;