If that's the case, one could argue that "even number, including the number zero" Then the hypothetical gas station attendant would argue that the instructions

If that's the case, one could argue that "even number, including the number zero" Then the hypothetical gas station attendant would argue that the instructions were self-contradictory and he was just doing his best to enforce them. It isn't just idiot-proofing, it's argument-proofing, making sure some self-important nit-picker doesn't disingenuously try to throw everything into chaos to prove that authority is stupid.