diff --git a/prototyping/Luau/StrictMode.agda b/prototyping/Luau/StrictMode.agda
index b6769f0..1b02804 100644
--- a/prototyping/Luau/StrictMode.agda
+++ b/prototyping/Luau/StrictMode.agda
@@ -5,18 +5,15 @@ module Luau.StrictMode where
 open import Agda.Builtin.Equality using (_≡_)
 open import FFI.Data.Maybe using (just; nothing)
 open import Luau.Syntax using (Expr; Stat; Block; BinaryOperator; yes; nil; addr; var; binexp; var_∈_; _⟨_⟩∈_; function_is_end; _$_; block_is_end; local_←_; _∙_; done; return; name; +; -; *; /; <; >; <=; >=; ··)
-open import Luau.Type using (Type; strict; nil; number; string; boolean; _⇒_; _∪_; _∩_; tgt)
+open import Luau.Type using (Type; nil; number; string; boolean; _⇒_; _∪_; _∩_; src; tgt)
 open import Luau.Subtyping using (_≮:_)
 open import Luau.Heap using (Heap; function_is_end) renaming (_[_] to _[_]ᴴ)
 open import Luau.VarCtxt using (VarCtxt; ∅; _⋒_; _↦_; _⊕_↦_; _⊝_) renaming (_[_] to _[_]ⱽ)
-open import Luau.TypeCheck(strict) using (_⊢ᴮ_∈_; _⊢ᴱ_∈_; ⊢ᴴ_; ⊢ᴼ_; _⊢ᴴᴱ_▷_∈_; _⊢ᴴᴮ_▷_∈_; var; addr; app; binexp; block; return; local; function; srcBinOp)
+open import Luau.TypeCheck using (_⊢ᴮ_∈_; _⊢ᴱ_∈_; ⊢ᴴ_; ⊢ᴼ_; _⊢ᴴᴱ_▷_∈_; _⊢ᴴᴮ_▷_∈_; var; addr; app; binexp; block; return; local; function; srcBinOp)
 open import Properties.Contradiction using (¬)
-open import Properties.TypeCheck(strict) using (typeCheckᴮ)
+open import Properties.TypeCheck using (typeCheckᴮ)
 open import Properties.Product using (_,_)
 
-src : Type → Type
-src = Luau.Type.src strict
-
 data Warningᴱ (H : Heap yes) {Γ} : ∀ {M T} → (Γ ⊢ᴱ M ∈ T) → Set
 data Warningᴮ (H : Heap yes) {Γ} : ∀ {B T} → (Γ ⊢ᴮ B ∈ T) → Set
 
diff --git a/prototyping/Luau/StrictMode/ToString.agda b/prototyping/Luau/StrictMode/ToString.agda
index 08ee13b..eee5722 100644
--- a/prototyping/Luau/StrictMode/ToString.agda
+++ b/prototyping/Luau/StrictMode/ToString.agda
@@ -7,8 +7,8 @@ open import FFI.Data.String using (String; _++_)
 open import Luau.Subtyping using (_≮:_; Tree; witness; scalar; function; function-ok; function-err)
 open import Luau.StrictMode using (Warningᴱ; Warningᴮ; UnallocatedAddress; UnboundVariable; FunctionCallMismatch; FunctionDefnMismatch; BlockMismatch; app₁; app₂; BinOpMismatch₁; BinOpMismatch₂; bin₁; bin₂; block₁; return; LocalVarMismatch; local₁; local₂; function₁; function₂; heap; expr; block; addr)
 open import Luau.Syntax using (Expr; val; yes; var; var_∈_; _⟨_⟩∈_; _$_; addr; number; binexp; nil; function_is_end; block_is_end; done; return; local_←_; _∙_; fun; arg; name)
-open import Luau.Type using (strict; number; boolean; string; nil)
-open import Luau.TypeCheck(strict) using (_⊢ᴮ_∈_; _⊢ᴱ_∈_)
+open import Luau.Type using (number; boolean; string; nil)
+open import Luau.TypeCheck using (_⊢ᴮ_∈_; _⊢ᴱ_∈_)
 open import Luau.Addr.ToString using (addrToString)
 open import Luau.Var.ToString using (varToString)
 open import Luau.Type.ToString using (typeToString)
diff --git a/prototyping/Luau/Type.agda b/prototyping/Luau/Type.agda
index 30c4538..59d1107 100644
--- a/prototyping/Luau/Type.agda
+++ b/prototyping/Luau/Type.agda
@@ -146,25 +146,16 @@ just T ≡ᴹᵀ just U with T ≡ᵀ U
 (just T ≡ᴹᵀ just T) | yes refl = yes refl
 (just T ≡ᴹᵀ just U) | no p = no (λ q → p (just-inv q))
 
-data Mode : Set where
-  strict : Mode
-  nonstrict : Mode
-
-src : Mode → Type → Type
-src m nil = never
-src m number = never
-src m boolean = never
-src m string = never
-src m (S ⇒ T) = S
--- In nonstrict mode, functions are covaraiant, in strict mode they're contravariant
-src strict    (S ∪ T) = (src strict S) ∩ (src strict T)
-src nonstrict (S ∪ T) = (src nonstrict S) ∪ (src nonstrict T)
-src strict    (S ∩ T) = (src strict S) ∪ (src strict T)
-src nonstrict (S ∩ T) = (src nonstrict S) ∩ (src nonstrict T)
-src strict never = unknown
-src nonstrict never = never
-src strict unknown = never
-src nonstrict unknown = unknown
+src : Type → Type
+src nil = never
+src number = never
+src boolean = never
+src string = never
+src (S ⇒ T) = S
+src (S ∪ T) = (src S) ∩ (src T)
+src (S ∩ T) = (src S) ∪ (src T)
+src never = unknown
+src unknown = never
 
 tgt : Type → Type
 tgt nil = never
diff --git a/prototyping/Luau/TypeCheck.agda b/prototyping/Luau/TypeCheck.agda
index aea6507..cabd27a 100644
--- a/prototyping/Luau/TypeCheck.agda
+++ b/prototyping/Luau/TypeCheck.agda
@@ -1,8 +1,6 @@
 {-# OPTIONS --rewriting #-}
 
-open import Luau.Type using (Mode)
-
-module Luau.TypeCheck (m : Mode) where
+module Luau.TypeCheck where
 
 open import Agda.Builtin.Equality using (_≡_)
 open import FFI.Data.Maybe using (Maybe; just)
@@ -10,15 +8,12 @@ open import Luau.Syntax using (Expr; Stat; Block; BinaryOperator; yes; nil; addr
 open import Luau.Var using (Var)
 open import Luau.Addr using (Addr)
 open import Luau.Heap using (Heap; Object; function_is_end) renaming (_[_] to _[_]ᴴ)
-open import Luau.Type using (Type; Mode; nil; unknown; number; boolean; string; _⇒_; tgt)
+open import Luau.Type using (Type; nil; unknown; number; boolean; string; _⇒_; src; tgt)
 open import Luau.VarCtxt using (VarCtxt; ∅; _⋒_; _↦_; _⊕_↦_; _⊝_) renaming (_[_] to _[_]ⱽ)
 open import FFI.Data.Vector using (Vector)
 open import FFI.Data.Maybe using (Maybe; just; nothing)
 open import Properties.Product using (_×_; _,_)
 
-src : Type → Type
-src = Luau.Type.src m
-
 orUnknown : Maybe Type → Type
 orUnknown nothing = unknown
 orUnknown (just T) = T
diff --git a/prototyping/Properties/StrictMode.agda b/prototyping/Properties/StrictMode.agda
index 1165fda..fd2cf2f 100644
--- a/prototyping/Properties/StrictMode.agda
+++ b/prototyping/Properties/StrictMode.agda
@@ -11,8 +11,8 @@ open import Luau.StrictMode using (Warningᴱ; Warningᴮ; Warningᴼ; Warning
 open import Luau.Substitution using (_[_/_]ᴮ; _[_/_]ᴱ; _[_/_]ᴮunless_; var_[_/_]ᴱwhenever_)
 open import Luau.Subtyping using (_≮:_; witness; unknown; never; scalar; function; scalar-function; scalar-function-ok; scalar-function-err; scalar-scalar; function-scalar; function-ok; function-err; left; right; _,_; Tree; Language; ¬Language)
 open import Luau.Syntax using (Expr; yes; var; val; var_∈_; _⟨_⟩∈_; _$_; addr; number; bool; string; binexp; nil; function_is_end; block_is_end; done; return; local_←_; _∙_; fun; arg; name; ==; ~=)
-open import Luau.Type using (Type; strict; nil; number; boolean; string; _⇒_; never; unknown; _∩_; _∪_; tgt; _≡ᵀ_; _≡ᴹᵀ_)
-open import Luau.TypeCheck(strict) using (_⊢ᴮ_∈_; _⊢ᴱ_∈_; _⊢ᴴᴮ_▷_∈_; _⊢ᴴᴱ_▷_∈_; nil; var; addr; app; function; block; done; return; local; orUnknown; srcBinOp; tgtBinOp)
+open import Luau.Type using (Type; nil; number; boolean; string; _⇒_; never; unknown; _∩_; _∪_; src; tgt; _≡ᵀ_; _≡ᴹᵀ_)
+open import Luau.TypeCheck using (_⊢ᴮ_∈_; _⊢ᴱ_∈_; _⊢ᴴᴮ_▷_∈_; _⊢ᴴᴱ_▷_∈_; nil; var; addr; app; function; block; done; return; local; orUnknown; srcBinOp; tgtBinOp)
 open import Luau.Var using (_≡ⱽ_)
 open import Luau.Addr using (_≡ᴬ_)
 open import Luau.VarCtxt using (VarCtxt; ∅; _⋒_; _↦_; _⊕_↦_; _⊝_; ⊕-lookup-miss; ⊕-swap; ⊕-over) renaming (_[_] to _[_]ⱽ)
@@ -23,13 +23,11 @@ open import Properties.Dec using (Dec; yes; no)
 open import Properties.Contradiction using (CONTRADICTION; ¬)
 open import Properties.Functions using (_∘_)
 open import Properties.Subtyping using (unknown-≮:; ≡-trans-≮:; ≮:-trans-≡; never-tgt-≮:; tgt-never-≮:; src-unknown-≮:; unknown-src-≮:; ≮:-trans; ≮:-refl; scalar-≢-impl-≮:; function-≮:-scalar; scalar-≮:-function; function-≮:-never; unknown-≮:-scalar; scalar-≮:-never; unknown-≮:-never)
-open import Properties.TypeCheck(strict) using (typeOfᴼ; typeOfᴹᴼ; typeOfⱽ; typeOfᴱ; typeOfᴮ; typeCheckᴱ; typeCheckᴮ; typeCheckᴼ; typeCheckᴴ)
+open import Properties.TypeCheck using (typeOfᴼ; typeOfᴹᴼ; typeOfⱽ; typeOfᴱ; typeOfᴮ; typeCheckᴱ; typeCheckᴮ; typeCheckᴼ; typeCheckᴴ)
 open import Luau.OpSem using (_⟦_⟧_⟶_; _⊢_⟶*_⊣_; _⊢_⟶ᴮ_⊣_; _⊢_⟶ᴱ_⊣_; app₁; app₂; function; beta; return; block; done; local; subst; binOp₀; binOp₁; binOp₂; refl; step; +; -; *; /; <; >; ==; ~=; <=; >=; ··)
 open import Luau.RuntimeError using (BinOpError; RuntimeErrorᴱ; RuntimeErrorᴮ; FunctionMismatch; BinOpMismatch₁; BinOpMismatch₂; UnboundVariable; SEGV; app₁; app₂; bin₁; bin₂; block; local; return; +; -; *; /; <; >; <=; >=; ··)
 open import Luau.RuntimeType using (RuntimeType; valueType; number; string; boolean; nil; function)
 
-src = Luau.Type.src strict
-
 data _⊑_ (H : Heap yes) : Heap yes → Set where
   refl : (H ⊑ H)
   snoc : ∀ {H′ a O} → (H′ ≡ᴴ H ⊕ a ↦ O) → (H ⊑ H′)
diff --git a/prototyping/Properties/Subtyping.agda b/prototyping/Properties/Subtyping.agda
index cc6bb5c..b713eaf 100644
--- a/prototyping/Properties/Subtyping.agda
+++ b/prototyping/Properties/Subtyping.agda
@@ -5,14 +5,12 @@ module Properties.Subtyping where
 open import Agda.Builtin.Equality using (_≡_; refl)
 open import FFI.Data.Either using (Either; Left; Right; mapLR; swapLR; cond)
 open import Luau.Subtyping using (_<:_; _≮:_; Tree; Language; ¬Language; witness; unknown; never; scalar; function; scalar-function; scalar-function-ok; scalar-function-err; scalar-scalar; function-scalar; function-ok; function-err; left; right; _,_)
-open import Luau.Type using (Type; Scalar; strict; nil; number; string; boolean; never; unknown; _⇒_; _∪_; _∩_; tgt)
+open import Luau.Type using (Type; Scalar; nil; number; string; boolean; never; unknown; _⇒_; _∪_; _∩_; src; tgt)
 open import Properties.Contradiction using (CONTRADICTION; ¬)
 open import Properties.Equality using (_≢_)
 open import Properties.Functions using (_∘_)
 open import Properties.Product using (_×_; _,_)
 
-src = Luau.Type.src strict
-
 -- Language membership is decidable
 dec-language : ∀ T t → Either (¬Language T t) (Language T t)
 dec-language nil (scalar number) = Left (scalar-scalar number nil (λ ()))
diff --git a/prototyping/Properties/TypeCheck.agda b/prototyping/Properties/TypeCheck.agda
index a5916a1..0726a4b 100644
--- a/prototyping/Properties/TypeCheck.agda
+++ b/prototyping/Properties/TypeCheck.agda
@@ -1,16 +1,14 @@
 {-# OPTIONS --rewriting #-}
 
-open import Luau.Type using (Mode)
-
-module Properties.TypeCheck (m : Mode) where
+module Properties.TypeCheck where
 
 open import Agda.Builtin.Equality using (_≡_; refl)
 open import Agda.Builtin.Bool using (Bool; true; false)
 open import FFI.Data.Maybe using (Maybe; just; nothing)
 open import FFI.Data.Either using (Either)
-open import Luau.TypeCheck(m) using (_⊢ᴱ_∈_; _⊢ᴮ_∈_; ⊢ᴼ_; ⊢ᴴ_; _⊢ᴴᴱ_▷_∈_; _⊢ᴴᴮ_▷_∈_; nil; var; addr; number; bool; string; app; function; block; binexp; done; return; local; nothing; orUnknown; tgtBinOp)
+open import Luau.TypeCheck using (_⊢ᴱ_∈_; _⊢ᴮ_∈_; ⊢ᴼ_; ⊢ᴴ_; _⊢ᴴᴱ_▷_∈_; _⊢ᴴᴮ_▷_∈_; nil; var; addr; number; bool; string; app; function; block; binexp; done; return; local; nothing; orUnknown; tgtBinOp)
 open import Luau.Syntax using (Block; Expr; Value; BinaryOperator; yes; nil; addr; number; bool; string; val; var; binexp; _$_; function_is_end; block_is_end; _∙_; return; done; local_←_; _⟨_⟩; _⟨_⟩∈_; var_∈_; name; fun; arg; +; -; *; /; <; >; ==; ~=; <=; >=)
-open import Luau.Type using (Type; nil; unknown; never; number; boolean; string; _⇒_; tgt)
+open import Luau.Type using (Type; nil; unknown; never; number; boolean; string; _⇒_; src; tgt)
 open import Luau.RuntimeType using (RuntimeType; nil; number; function; string; valueType)
 open import Luau.VarCtxt using (VarCtxt; ∅; _↦_; _⊕_↦_; _⋒_; _⊝_) renaming (_[_] to _[_]ⱽ)
 open import Luau.Addr using (Addr)
@@ -22,9 +20,6 @@ open import Properties.Equality using (_≢_; sym; trans; cong)
 open import Properties.Product using (_×_; _,_)
 open import Properties.Remember using (Remember; remember; _,_)
 
-src : Type → Type
-src = Luau.Type.src m
-
 typeOfᴼ : Object yes → Type
 typeOfᴼ (function f ⟨ var x ∈ S ⟩∈ T is B end) = (S ⇒ T)