You may remind or remember: such combinations of switches can be found in the household, the one at the ends of a longer corridor, the other by fuse and lamp switch (or as safety switch at an electric garden tool to prevent from cutting-off your own fingers).
Instead of up and down, on and off we now use short `'abstract' symbols - I suggest line and circle, and the switches may become A and B, the lamps D and E.
Thus we get a handsome table:
A
B
D
E
O
O
O
O
O
I
O
I
I
O
O
I
I
I
I
O
Please don't tell my secret now - these symbols circle and line are similar to the cyphersymbols 0 and 1 - but it is really not important what I take, the two signs only must be different.