C# discriminated union type

Union.cs

// adapted from : http://stackoverflow.com/questions/3151702/discriminated-union-in-c-sharp by Juliet
    public abstract class Union<TA, TB, TC>
    {
        public static Case1 Create(TA x) { return new Case1(x);}
        public static Case2 Create(TB x) { return new Case2(x);}
        public static Case3 Create(TC x) { return new Case3(x);}

        public abstract T Match<T>(Func<TA, T> f, Func<TB, T> g, Func<TC, T> h);
        private Union() { }

        public sealed class Case1 : Union<TA, TB, TC>
        {
            public readonly TA Item;
            public Case1(TA item) { Item = item; }
            public override T Match<T>(Func<TA, T> f, Func<TB, T> g, Func<TC, T> h)
            {
                return f(Item);
            }
        }

        public sealed class Case2 : Union<TA, TB, TC>
        {
            public readonly TB Item;
            public Case2(TB item) { Item = item; }
            public override T Match<T>(Func<TA, T> f, Func<TB, T> g, Func<TC, T> h)
            {
                return g(Item);
            }
        }

        public sealed class Case3 : Union<TA, TB, TC>
        {
            public readonly TC Item;
            public Case3(TC item) { Item = item; }
            public override T Match<T>(Func<TA, T> f, Func<TB, T> g, Func<TC, T> h)
            {
                return h(Item);
            }
        }
    }

    // adapted from : http://stackoverflow.com/questions/3151702/discriminated-union-in-c-sharp by Juliet
    public abstract class Union<TA, TB>
    {
        public static Case1 Create(TA x) { return new Case1(x);}
        public static Case2 Create(TB x) { return new Case2(x);}

        public abstract void Match(Action<TA> f, Action<TB> g);
        public abstract T Match<T>(Func<TA, T> f, Func<TB, T> g);

        private Union() { }

        public sealed class Case1 : Union<TA, TB>
        {
            public readonly TA Item;
            public Case1(TA item) { Item = item; }
            public override void Match(Action<TA> f, Action<TB> g)
            {
                f(Item);
            }
            public override T Match<T>(Func<TA, T> f, Func<TB, T> g)
            {
                return f(Item);
            }
        }

        public sealed class Case2 : Union<TA, TB>
        {
            public readonly TB Item;
            public Case2(TB item) { Item = item; }
            public override void Match(Action<TA> f, Action<TB> g)
            {
                g(Item);
            }
            public override T Match<T>(Func<TA, T> f, Func<TB, T> g)
            {
                return g(Item);
            }
        }
    }