namespace System { internal static class MemoryExtensionsPolyfills { public static bool Contains<T>(this ReadOnlySpan<T> span, T value) where T : IEquatable<T>; public static bool ContainsAnyExcept(this ReadOnlySpan<char> span, char value); public static bool ContainsAny(this ReadOnlySpan<char> span, ReadOnlySpan<char> values); } }