implement boolean function using half adders and not gates

Question

I received this question from my lecturer and i am stuck.

F=ca+b'a'

implement this function using no more than 3 HA (half adder) and 3 NOT gates.

i succeed to get a'b' and ac and still had 1 HA and 1 NOT gate.

I have difficulties creating the OR gate for those two.

Answer 1

Use De Morgan's law and convert the expression in the following form :- ((ca)'(b'a')')' . Assuming that complements of the Literals are available. The actual implementation of the circuit.