scheme :: ALTCAT_2:sch 3
ValOnSingletons{ F₁() -> non empty set , F₂() -> Function, F₃() -> Element of F₁(), F₄( set ) -> set , P₁[ set ] } :

F₂() . F₃() = F₄(F₃())

provided

A1: F₂() = { [o,F₄(o)] where o is Element of F₁() : P₁[o] } and
A2: P₁[F₃()]