The circuit shown below has 4 boxes described by input P,

The circuit shown below has 4 boxes described by input P, Q, R and output Y, Z, Y = P ⊕ Q &olplus; R and Z = R Q + P R + Q P.

The circuit act as a 4 bit—

1. adder giving P + Q
2. subtractor giving P – Q
3. subtractor giving Q – P
4. adder giving P + Q + R

Since given Y = P ⊕ Q ⊕ R
and Z = RQ + PR + QP
which represents a subtractor circuit.