/// <summary>
/// <para>Emits true and completes on completion if all items emitted satisfy predicate, or false and
/// completes imediately if the predicate fails on any item</para>
///
/// <para>All implementation using Where, Select and FirstOrDefault</para>
/// </summary>
public static IObservable <bool> Contains <T>(this IObservable <T> source, T item)
{
var comparer = Comparer <T> .Default;
return(source.Any((t, i) => comparer.Compare(t, item) >= 0));
}
