AKA Subtractor.
The 2 resistors on the right represent R1, and the 2 resistors on the left represent R2.
The voltage source on the most left is V2.
The voltage source on the most right is V1.
V+ = V1(R1/(R1 + R2))
V- = V2 + (Vo - V2)(R2/(R2 + R1))
Vo = (V1 - V2)(R1/R2)
If R1 = R2, Vo = (V1-V2)
Play around ;)
