f<=((NOT A) AND (NOT C)) OR ((NOT A) AND B AND D)
   OR (A AND C AND (NOT D)) OR ((NOT B) AND (NOT C) AND (NOT D)); 


D<= '0', '1' after 10ns, '0' after 20ns, '1' after 30ns, '0' after 40ns, 
         '1' after 50ns, '0' after 60ns, '1' after 70ns, '0' after 80ns, 
         '1' after 90ns, '0' after 100ns, '1' after 110ns, '0' after 120ns, 
         '1' after 130ns, '0' after 140ns, '1' after 150ns, '0' after 160ns;
C<= '0', '1' after 20ns, '0' after 40ns, '1' after 60ns, '0' after 80ns, 
         '1' after 100ns, '0' after 120ns, '1' after 140ns, '0' after 160ns;
B<= '0', '1' after 40ns, '0' after 80ns, '1' after 120ns, '0' after 160ns; 
A<= '0', '1' after 80ns, '0' after 160ns;