[math-fun] Penrose local isomorphism theorem

Can anyone provide a reference for Penrose's "local isomorphism theorem", asserting that every Penrose tiling looks like every other? I seem to recall hearing a strong version of this stated once, to the effect that if you have a pattern of diameter n in one Penrose tiling, and you look for that pattern in a second Penrose tiling, you won't have to travel further than distance 2n. Jim Propp