Pair represents a pair of values. This is equivalent to a Tuple of length two, the Separated type in fp-ts, and any other type that contains exactly two covariant other types.

The primary use fo Pair in this library is the target of a partition, where some type A is partitioned, either into [A, A], or [A, B] where B extends A.

Other uses will likely come when Arrows are implemented in fun.