public static Stream <T> Calm <T>(this Stream <T> s, IEqualityComparer <T> comparer) => s.CalmImpl(comparer.Equals);
public static Stream <T> Calm <T>(this Stream <T> s, Func <T, T, bool> areEqual) => s.CalmImpl(areEqual);
public static Stream <T> Calm <T>(this Stream <T> s) => s.CalmImpl(EqualityComparer <T> .Default.Equals);