public static Fin <B> bind <A, B>(Fin <A> ma, Func <A, Fin <B> > f) => ma.Bind(f);
public static Fin <Fin <B> > Traverse <A, B>(this Fin <Fin <A> > ma, Func <A, B> f) => ma.Bind(a => a.Map(f));
public static Fin <R> flatten <R>(Fin <Fin <R> > ma) => ma.Bind(identity);