∀[s:Name]. ∀[avoid:Name List]. (maybe-new(s;avoid) ∈ {s':Name| ¬(s' ∈ avoid)} )
{ ProveWfLemma }
1. s : Name
2. avoid : Name List
3. (s ∈ avoid)
⊢ s @ nat-to-str(mu(λn.(¬bs @ nat-to-str(n) ∈b avoid))) ∈ {s':Name| ¬(s' ∈ avoid)}