list : (α -> bool) -> α list -> bool⊢ ∀A. list A = {l | ∀e. MEM e l ⇒ e ∈ A}
⊢ countable 𝕌(:α) ⇒ countable 𝕌(:α list)
⊢ FINITE 𝕌(:α) ⇒ countable 𝕌(:α list)
⊢ INFINITE A ⇒ list A ≈ A
⊢ 𝕌(:α list) = list 𝕌(:α)
⊢ list A ≈ BIGUNION (IMAGE (λn. {n} × A ** count n) 𝕌(:num))
⊢ list ∅ = {[]}
⊢ list {e} ≈ 𝕌(:num)
⊢ A ** count n ≈ {l | LENGTH l = n ∧ ∀e. MEM e l ⇒ e ∈ A}