3+3=2 in a modulo 4 ring. You say "who cares about that?" OK, 3+3=2 in a data field represented by only 2 bits. At least some of us here have actually run in

3+3=2 in a modulo 4 ring. You say "who cares about that?" OK, 3+3=2 in a data field represented by only 2 bits. At least some of us here have actually run into such things. [Edit to add: And if you don't care about it in 2 bits, you at least need to know about that it can happen in 32 bits.]