What is the equivalent resistance when resistors are in a cube?

The equivalent resistance, from corner to corner, of 12 resistors connected in a cube is 5/6 that of a single resistor.

Proof:

Start from one corner and flow current through to the opposite corner. You have three resistors. Each of those three resistors is connected to two resistors, in a crisscross pattern. Those six resistors are then connected to three resistors which are connected to the other corner. By symmetry, the voltages at the upper junctions are the same, and then same can be said for the lower junction. You can then simplify the circuit by shorting out the upper junctions and (separately) the lower junctions. This means the circuit is equivalent to three resistors in parallel, in series with six resistors in parallel, in series with three resistors in parallel. This is 1/3 R plus 1/6 R plus 1/3 R, or 5/6 R.