/// <summary>
/// Equivalent to <see cref="IFunctor{TSource}.Map{TResult}(Func{TSource, TResult})"/>, but restricted to <see cref="Memo{TState, TKey, TValue}"/>. Offers LINQ query support with one <c>from</c>-clause.
/// </summary>
/// <typeparam name="TState">The type of the state.</typeparam>
/// <typeparam name="TKey">The key of the memoization.</typeparam>
/// <typeparam name="TSource">The type of the source's value.</typeparam>
/// <param name="source">The source.</param>
/// <param name="f">The function to apply.</param>
public static Memo <TState, TKey, TSource> Select <TState, TKey, TSource>(this Memo <TState, TKey, TSource> source, Func <TSource, TSource> f)
where TState : IDictionary <TKey, TSource>
=> (Memo <TState, TKey, TSource>)source.MonoMap(f);