private static INotifyCollectionChanged getSource(
INotifyCollectionChanged source1,
IReadScalar <INotifyCollectionChanged> source2Scalar,
IEqualityComparer <TSourceItem> equalityComparer)
{
return(source1
.GroupJoining <TSourceItem, TSourceItem, TSourceItem>(
source2Scalar, item1 => item1, item2 => item2, equalityComparer)
.Filtering(jg => jg.Count > 0)
.Selecting(jg => jg.OuterItem));
}
