Bij(ℕ;ℕ × ℕ;λx.coded-pair(x))
{ TACTIC:(RepeatFor 2 ((D 0 THEN Auto)) THEN All Reduce) }
1. a1 : ℕ@i
2. a2 : ℕ@i
3. coded-pair(a1) = coded-pair(a2) ∈ (ℕ × ℕ)
⊢ a1 = a2 ∈ ℕ
1. b : ℕ × ℕ@i
⊢ ∃a:ℕ. (coded-pair(a) = b ∈ (ℕ × ℕ))