the stage l = def (l) uses formulas with parameters from l to define the sets x and y. if one discounts (for the moment) the parameters, the formulas can be given a standard gödel numbering by the natural numbers. if φ is the formula with the smallest gödel number that can be used to define x, and ψ is the formula with the smallest gödel number that can be used to define y, and ψ is different from φ, then let x<y if and only if φ<ψ in the gödel numbering. henceforth, we suppose that ψ=φ.