Consider a black box for a function f : {0,1} -> {0,1} with the goal to determine f(0) ⊕ f(1) with one query to f.

Create a quantum circuit that builds the following two-qubit state with one query to f:
1/√3(((-1)^f(0))|00>+((-1)^f(1))|01>+|11>)

Then create a quantum algorithm using only unitary operations and standard measurements with one query to f. It should succeed with probability 1 if f(0) V f(1) = 0, and probability 8/9 if f(0) V f(1) = 1.