lhs test

========

`unsplit` is an arrow that takes a pair of values and combines them to

return a single value:

> unsplit :: (Arrow a) => (b -> c -> d) -> a (b, c) d

> unsplit = arr . uncurry

>           -- arr (\op (x,y) -> x `op` y)

`(***)` combines two arrows into a new arrow by running the two arrows on a

pair of values (one arrow on the first item of the pair and one arrow on the

second item of the pair).

    f *** g = first f >>> second g

Block quote:

 > foo bar