public static Either <CollTo, Right> mapLeftC <CollFrom, CollTo, Right, ElemFrom, ElemTo>(
this Either <CollFrom, Right> e,
Fn <ElemFrom, ElemTo> mapper,
Fn <IEnumerable <ElemTo>, CollTo> toCollection
)
where CollFrom : IEnumerable <ElemFrom>
where CollTo : IEnumerable <ElemTo>
=> e.mapLeftC(mapper).mapLeft(toCollection);
