namespace System.Collections.Immutable { public sealed class ImmutableStack<T> : IImmutableStack<T>, IEnumerable<T>, IEnumerable { public struct Enumerator { public T Current { get; } public bool MoveNext(); } public static ImmutableStack<T> Empty { get; } public bool IsEmpty { get; } public ImmutableStack<T> Clear(); public T Peek(); public ImmutableStack<T> Push(T value); public ImmutableStack<T> Pop(); public ImmutableStack<T> Pop(out T value); public Enumerator GetEnumerator(); } }