a-foundation/src/main/java/com/ajjpj/afoundation/collection/immutable/MapAsSetWrapper.java
@SuppressWarnings ("unchecked")
    protected <X> ASet<X> createInternal (Iterable<X> elements) {
        AMap result = inner.clear ();

        for (X el: elements) {
            result = result.updated (el, Boolean.TRUE);
        }
        return (ASet) wrapAsSet (result);
    }
@SuppressWarnings ("unchecked")
    protected <X> ASet<X> createInternal (Iterable<X> elements) {
        AMap result = inner.clear ();

        for (X el: elements) {
            result = result.updated (el, Boolean.TRUE);
        }
        return (ASet) wrapAsSet (result);
    }
-------------------------------------- collection transformations