public Tuple <Either <U, T>, string[]> AsSuccessOrFailure <U>(Func <Array1 <string>, U> forFailure) => Tuple.Create(TerminalOrValue.Map(forFailure, t => t), NonTerminalWarnings);
public static Either <U, U> Select <T, U>(this Either <T, T> e, Func <T, U> f) => e.Map(f, f);