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+open import Data.Nat
+open import Relation.Binary.PropositionalEquality
+
+variable m n : ℕ
+
+data Term : ℕ → Set where
+  zero : Term (suc n)
+  suc : Term n → Term (suc n)
+
+variable t u : Term n
+
+data Weak : ℕ → Set where
+  wk : Weak (suc n)
+  suc : Weak n → Weak (suc n)
+
+data Subst : ℕ → Set where
+  <_> : Term n → Subst n
+  suc : Subst n → Subst (suc n)
+
+_[_]t : Term n → Weak n → Term (suc n)
+t [ wk ]t = suc t
+zero [ suc w ]t = zero
+suc t [ suc w ]t = suc (t [ w ]t)
+
+{-
+0  -> 0
+1  -> 2
+2  -> 3
+
+suc wk
+
+
+wk
+0 -> 1
+1 -> 2
+2 -> 3
+-}
+
+_s[_]t : Term (suc n) → Subst n → Term n
+zero s[ < u > ]t = u
+suc t s[ < u > ]t = t
+zero s[ suc s ]t = zero
+suc t s[ suc s ]t = suc (t s[ s ]t)
+
+{-
+x,y,z  --> x,z
+0,1,2  y => x,z ⊢ t 
+
+x => x  0 => 0
+y => t  1 => t
+z => z  2 => 1
+
+
+-}
+
+infix 15 _⇒_
+
+data Form : ℕ → Set where
+  _⇒_ : Form n → Form n → Form n
+  ∀F : Form (suc n) → Form n
+  P : Term n → Form n
+--  R : Term n → Term n → Form n
+
+_[_]F : Form n → Weak n → Form (suc n)
+(A ⇒ B) [ w ]F = (A [ w ]F) ⇒ (B [ w ]F)
+∀F A [ w ]F = ∀F (A [ suc w ]F)
+P a [ w ]F = P (a [ w ]t )
+
+_s[_]F : Form (suc n) → Subst n → Form n
+(A ⇒ B) s[ s ]F = (A s[ s ]F) ⇒ (B s[ s ]F)
+∀F A s[ s ]F = ∀F (A s[ suc s ]F)
+P a s[ s ]F = P (a s[ s ]t )
+
+infix 10 _▷_
+
+data Con : ℕ → Set where
+  • : Con n
+  _▷_ : Con n → Form n → Con n
+
+_[_]C : Con n → Weak n → Con (suc n)
+• [ w ]C = •
+(Γ ▷ A) [ w ]C = (Γ [ w ]C) ▷ (A [ w ]F)
+
+variable Γ Δ : Con n
+variable A B C : Form n
+
+infix 5 _⊢_ 
+
+data _⊢_ : Con n → Form n → Set where
+  zero : Γ ▷ A ⊢ A
+  suc : Γ ⊢ A → Γ ▷ B ⊢ A
+  lam : Γ ▷ A ⊢ B → Γ ⊢ A ⇒ B
+  app : Γ ⊢ A ⇒ B → Γ ⊢ A → Γ ⊢ B
+  Lam : Γ [ wk ]C ⊢ A → Γ ⊢ ∀F A
+  App : Γ ⊢ ∀F A → (t : Term _) → Γ ⊢ A s[ < t > ]F
+
+-- (A ⇒ ∀ x . P x) ⇒ ∀ x . A → P x
+
+-- A ≡ A [ wk ][ < t > ] 
+
+wk-subst :  (A [ wk ]F) s[ < t > ]F ≡ A
+wk-subst = {!!}
+
+example : • ⊢ (A ⇒ (∀F (P zero))) ⇒ (∀F (A [ wk ]F) ⇒ P zero)
+example {A = A} = lam (lam (App (app (suc zero) 
+         (subst (λ X → (• ▷ A ⇒ ∀F (P zero)) ▷ ∀F (A [ wk ]F) ⊢ X)
+           (wk-subst {A = A}) (App zero zero))) zero))
+
+