Build two input-lanes. A lever can be used as power-source.
Place three blocks behind the input lanes, like you can see in the picture.
Place redstone-torches on the other side of the blocks.
Place two blocks over the two torches at the border.
Connect those two blocks with Redstone.
Install two redstone-lanes, starting at the border-redstone-torches.
Invert the signal by placing a block at the end of the lane and…
…by adding a redstone torch at the back of these two blocks.
Connect the signal of the torches to get the output-lane.
So all in all, only if both inputs are different, the output becomes positive.