Quantum Computing.
concatenating CNOT and Toffoli one can get a simplified adder gate. Since U_CNOT = |000⟩⟨000| + |001⟩⟨001| + |010⟩⟨010| + |011⟩⟨011| + |110⟩⟨100| + |111⟩⟨101| + |100⟩⟨110|+ |101⟩⟨111| the combination is U_T U_CNOT = |000⟩⟨000| + |001⟩⟨001| + |010⟩⟨010| + |011⟩⟨011| + |110⟩⟨100| + |111⟩⟨101| +