there is a formula of set theory that expresses the idea that x=l. it has only free variables for x and α. using this we can expand the definition of each constructible set. if s∈l, then s = {y|y∈l and φ(y,z...,z) holds in (l,∈)} for some formula φ and some z...,z in l. this is equivalent to saying that: for all y, y∈s if and only if [there exists x such that x=l and y∈x and ψ(x,y,z...,z)] where ψ(x...) is the result of restricting each quantifier in