“NAND-Gate” in Minecraft (Not-And-Gate)

Place two blocks next to each other (distance: one block). Install two redstone-lanes (both connected to a lever) which end in these blocks.
nicht_und_gatter-1

Put two redstone-torches on the other side of these blocks and extract the signal of the torches by connecting the redstone-lanes.
nicht_und_gatter-2

Build another block right next to the extracted signal, and put a redstone torch at its back, too.
nicht_und_gatter-3


Explanation:
The output-signal becomes positive if one or both inputs are negative (NOT-AND=Not both inputs are positive).