diff --git a/Tactic/Simp.agda b/Tactic/Simp.agda
new file mode 100644
index 00000000..abadee30
--- /dev/null
+++ b/Tactic/Simp.agda
@@ -0,0 +1,172 @@
+-- Need a dictionary of theorems. How to extend it?
+-- What's a reasonable strategy to rewrite with? How much should we reduce?
+-- Currently requires `--lossy-unification`. To drop that requirement, we'd need to implement our own unification (or ask for Agda to give us a lossy `unify` TC primitive).
+-- TODO: rewrite multiple times
+-- TODO: rewrite subexpressions
+
+{-# OPTIONS -v allTactics:100 #-}
+{-# OPTIONS --lossy-unification #-}
+
+module Tactic.Simp where
+
+open import Class.DecEq
+open import Class.Functor
+open import Class.MonadReader.Instances
+open import Class.MonadTC.Instances
+open import Class.Show
+open import Class.Traversable
+
+open import Data.Bool
+open import Data.Maybe hiding (_>>=_; map; zip)
+open import Data.Unit
+open import Data.List
+open import Data.Nat
+open import Data.Nat.Properties
+open import Data.Product hiding (map; zip)
+
+open import Data.String hiding (show; map; head; replicate; _==_; length) renaming (_++_ to _++S_)
+
+open import Function
+
+open import Relation.Binary.PropositionalEquality
+
+open import Meta.Init
+open import Reflection.Utils hiding (args)
+open import Reflection.Tactic
+
+open import Effect.Monad.State
+open import Effect.Monad
+
+open import Class.Monoid
+open import Class.Monad
+open import Class.MonadError
+
+open import Reflection.Utils.TCI using (applyWithVisibility)
+
+open import Meta.Prelude
+
+open MonadError ⦃...⦄
+
+_`$_ : Term → Term → Term
+t `$ t' = quote _$_ ∙⟦ t ∣ t' ⟧
+
+_`$ⁿ_ : Term → List Term → Term
+t `$ⁿ []       = t
+t `$ⁿ (x ∷ t') = (t `$ x) `$ⁿ t'
+
+`λⁿ : ℕ → Term → Term
+`λⁿ zero    t = t
+`λⁿ (suc n) t = `λ "" ⇒ `λⁿ n t
+
+NDict = List Name
+
+testDict : NDict
+testDict = quote +-assoc ∷ quote +-identityˡ ∷ quote +-identityʳ ∷ []
+
+-- traverseState : {A B S : Set} → (A → State S B) → List A → State S (List B)
+-- traverseState = {!!}
+
+-- Matchee → Template → Maybe (List Term)
+
+replicateM : {A : Set} → ℕ → TC A → TC (List A)
+replicateM n x = sequence (replicate n x)
+
+matchTerms : (freeVars : ℕ) → Term → Term → TC (Maybe (List Term))
+matchTerms fv t templ = runSpeculative do
+  metas ← replicateM fv (newMeta unknown)
+  debugLog1 t
+  --extendContext' (zipWithIndex (λ i x → (("x" ++S show i) , vArg x)) metas) do
+  debugLog ("Match:\n" ∷ᵈ t ∷ᵈ "\nand\n" ∷ᵈ (`λⁿ fv templ) `$ⁿ metas ∷ᵈ [])
+  catch
+    (unify t ((`λⁿ fv templ) `$ⁿ metas) >> debugLog1 "Success" >> return (just metas , true))
+    (λ _ → return (nothing , false))
+
+-- case runState (helper 0 fv t templ) (replicate fv nothing) of λ where
+--     (s , true)  → nothing -- term/variable assignment conflict
+--     (s , false) → let res = catMaybes s in if length res == fv then just res else nothing
+--   where
+--     open RawMonad (monad {S = List (Maybe Term)}) hiding (zip)
+
+    -- helper : ℕ → (freeVars : ℕ) → Term → Term → State (List (Maybe Term)) Bool
+    -- helper n fv (var x args) (var x₁ args₁) = {!traverse!}
+    -- helper n fv (con c args) (con c₁ args₁) = if (c == c₁) ∧ (length args == length args₁)
+    --   then (do
+    --     traverseState {!(λ where (arg _ t , arg _ t') → helper n fv t t')!} (zip args args₁)
+    --     return false)
+    --   else return true
+    -- helper n fv (def f args) (def f₁ args₁) = {!!}
+    -- helper n fv (lam v t) (lam v₁ t₁) = {!!}
+    -- helper n fv (pat-lam cs args) (pat-lam cs₁ args₁) = {!!}
+    -- helper n fv (pi a b) (pi a₁ b₁) = {!!}
+    -- helper n fv (sort s) (sort s₁) = {!!}
+    -- helper n fv (lit l) (lit l₁) = {!!}
+    -- helper n fv (meta x x₁) (meta x₂ x₃) = {!!}
+    -- helper n fv unknown unknown = return false
+    -- helper n fv _ _ = return true
+
+data Instantiated : Set where
+  isInst notInst : Instantiated
+
+Instantiation : Instantiated → Set
+Instantiation isInst  = List Term
+Instantiation notInst = ℕ
+
+record Equation (i : Instantiated) : Set where
+  field lhs rhs : Term
+        name : Name
+        args : Instantiation i
+
+EqDict = List (Equation notInst)
+
+preprocessDict : NDict → TC EqDict
+preprocessDict d = traverse genEq d
+  where
+   removePis : Term → Term × ℕ
+   removePis (pi a (abs _ b)) = map₂ suc (removePis b)
+   removePis t = (t , 0)
+
+   genEq : Name → TC (Equation notInst)
+   genEq n = do
+     ty ← getType n >>= reduce
+     (def (quote _≡_) (hArg l ∷ hArg T ∷ vArg lhs ∷ vArg rhs ∷ []) , args) ← return $ removePis ty
+       where (ty , _) → error1 ("Error while preprocessing simp dict: Not an equation:" <+> show ty)
+     return record { lhs = lhs ; rhs = rhs ; name = n ; args = args }
+
+-- look up a rule in the dictionary & unify with a given type
+findAndUnify : EqDict → Type → TC (Maybe (Equation isInst))
+findAndUnify d ty = do
+  ty ← reduce ty
+  res ← traverse (λ where eq@record { args = args ; lhs = lhs } → matchTerms args ty lhs >>= return ∘ (_, eq)) d
+  return $ head (extractMatch res)
+  where
+    extractMatch : List (Maybe (List Term) × Equation notInst) → List (Equation isInst)
+    extractMatch [] = []
+    extractMatch ((just x , eq) ∷ l) = (record { Equation eq ; args = x }) ∷ extractMatch l
+    extractMatch ((nothing , _) ∷ l) = extractMatch l
+
+extractRewrite : Equation isInst → TC Term
+extractRewrite record { name = n ; args = a } = applyWithVisibility n a
+
+simp1Test : EqDict → Type → TC ⊤
+simp1Test d ty = do
+  just res ← findAndUnify d ty
+    where nothing → error1 "Couldn't find a rewrite rule!"
+  res ← extractRewrite res
+  debugLog1 res
+  unifyWithGoal res
+
+private
+  open import Tactic.Derive.TestTypes
+  open import Tactic.Defaults
+
+  testDict' : EqDict
+  testDict' = byTC (preprocessDict testDict)
+
+  testTerm : ℕ → ℕ → Term
+  testTerm x y = quoteTerm ((x + 0) + y)
+
+  testTerm' : ℕ → ℕ → Term
+  testTerm' x y = quoteTerm (x + (0 + y))
+
+  test : ∀ {x y : ℕ} → (x + 0) + y ≡ x + (0 + y)
+  test {x} {y} = by (simp1Test testDict' (quoteTerm ((x + 0) + y)))