[Haskell-cafe] Textbook example of instance Foldable ((,) a)

[Manuel Schneckenreither]

    >>>>> "HT" == Henning Thielemann <lemming at henning-thielemann.de> writes:

    HT> "length (a,b) == 1" is only a consequence of defining instance
    HT> Foldable for pairs. It was not the argument to implement that
    HT> instance, at all.

What was the argument to use 1, not 2 for instance?