Let x0 of type ι be given.
Let x1 of type ι → ι → ο be given.
Let x2 of type ι → ι → ο be given.
Let x3 of type ι → ι → ο be given.
Let x4 of type ι → ι → ο be given.
Assume H0:
∀ x5 . x5 ∈ x0 ⟶ ∀ x6 . x6 ∈ x0 ⟶ iff (x1 x5 x6) (x2 x5 x6).
Assume H1:
∀ x5 . x5 ∈ x0 ⟶ ∀ x6 . x6 ∈ x0 ⟶ iff (x3 x5 x6) (x4 x5 x6).
Apply encode_r_ext with
x0,
x1,
x2.
The subproof is completed by applying H0.
Apply L2 with
λ x5 x6 . lam 3 (λ x7 . If_i (x7 = 0) x0 (If_i (x7 = 1) (encode_r x0 x1) (encode_r x0 x3))) = lam 3 (λ x7 . If_i (x7 = 0) x0 (If_i (x7 = 1) x5 (encode_r x0 x4))).
Apply encode_r_ext with
x0,
x3,
x4.
The subproof is completed by applying H1.
Apply L3 with
λ x5 x6 . lam 3 (λ x7 . If_i (x7 = 0) x0 (If_i (x7 = 1) (encode_r x0 x1) (encode_r x0 x3))) = lam 3 (λ x7 . If_i (x7 = 0) x0 (If_i (x7 = 1) (encode_r x0 x1) x5)).
Let x5 of type ι → ι → ο be given.
The subproof is completed by applying H4.