use constraints when checking δ

when checking δ 𝑖 ⇒ s, add 𝑖=ε to Ψ instead of checking s‹ε/𝑖›.
this has the same effect but an error message will show "𝑖, 𝑖=ε" in
the context

lib/Quox/Typechecker.idr

@@ -196,12 +196,15 @@ mutual
 
   check' ctx sg (DLam body) ty = do
     (ty, l, r) <- expectEq !ask ctx ty
+    let ctx' = extendDim body.name ctx
+        ty   = ty.term
+        body = body.term
     -- if Ψ, i | Γ ⊢ σ · t ⇐ A ⊳ Σ
-    qout <- checkC (extendDim body.name ctx) sg body.term ty.term
-    -- if Ψ | Γ ⊢ t‹0› = l : A‹0›
-    equal ctx ty.zero body.zero l
-    -- if Ψ | Γ ⊢ t‹1› = r : A‹1›
-    equal ctx ty.one body.one  r
+    qout <- checkC ctx' sg body ty
+    -- if Ψ, i, i = 0 | Γ ⊢ t = l : A
+    equal (eqDim (BV 0) (K Zero) ctx') ty body (dweakT 1 l)
+    -- if Ψ, i, i = 1 | Γ ⊢ t = r : A
+    equal (eqDim (BV 0) (K One)  ctx') ty body (dweakT 1 r)
     -- then Ψ | Γ ⊢ σ · (δ i ⇒ t) ⇐ Eq [i ⇒ A] l r ⊳ Σ
     pure qout