A system for representing natural numbers inductively using only two symbols, "0" (zero) and "S" (successor). This could be expressed as a recursive data type with the following Haskell definition: data Peano = Zero | Succ Peano The number three, usually written "SSS0", would be Succ (Succ (Succ Zero)). Addition of Peano numbers can be expressed as a simple syntactic transformation: pLUs Zero n = n pLUs (Succ m) n = Succ (pLUs m n) (1995-03-28)