public static void Zip1a()
{
IEnumerable <int> first = new ThrowingEnumerable <int>();
var second = Enumerable.Range(0, 1);
Func <int, int, Either <int, int> > resultSelector = (i, j) => Either <int, int> .OfLeft(i + j);
var q = Assert.DoesNotThrow(() => Either.Zip(first, second, resultSelector));
q.OnLeft(x => Assert.ThrowsOnNext(x));
q.OnRight(x => Assert.Fail());
}