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w'xy + wz + xz + w'y'z + w'xy' + wx'z = wz + w'x + xz +w'y'z = wz + w'x + w'y'z since wz $ w'x = xz But wz +w'y'z = z(w + w'y') = z(w + y') = wz + w'x + y'z