diff --git a/spectec/src/exe-spectec/main.ml b/spectec/src/exe-spectec/main.ml
index ae86b09d9e..3a52c7a05a 100644
--- a/spectec/src/exe-spectec/main.ml
+++ b/spectec/src/exe-spectec/main.ml
@@ -27,6 +27,7 @@ type pass =
   | AliasDemut
   | ImproveIds
   | Ite
+  | PatSimp
 
 (* This list declares the intended order of passes.
 
@@ -44,6 +45,7 @@ let all_passes = [
   Uncaseremoval;
   Sideconditions;
   SubExpansion;
+  PatSimp;
   Sub;
   AliasDemut;
   ImproveIds
@@ -112,6 +114,7 @@ let pass_flag = function
   | Uncaseremoval -> "uncase-removal"
   | ImproveIds -> "improve-ids"
   | Ite -> "ite"
+  | PatSimp -> "pattern-simp"
 
 let pass_desc = function
   | Sub -> "Synthesize explicit subtype coercions"
@@ -126,6 +129,7 @@ let pass_desc = function
   | AliasDemut -> "Lifts type aliases out of mutual groups"
   | ImproveIds -> "Disambiguates ids used from each other"
   | Ite -> "If-then-else introduction"
+  | PatSimp -> "Simplifies non-linear and definite iteration patterns"
 
 
 let run_pass : pass -> Il.Ast.script -> Il.Ast.script = function
@@ -141,7 +145,7 @@ let run_pass : pass -> Il.Ast.script -> Il.Ast.script = function
   | AliasDemut -> Middlend.AliasDemut.transform
   | ImproveIds -> Middlend.Improveids.transform
   | Ite -> Middlend.Ite.transform
-
+  | PatSimp -> Middlend.PatSimp.transform
 
 (* Argument parsing *)
 
diff --git a/spectec/src/il/walk.ml b/spectec/src/il/walk.ml
index d8d1d3e014..4a471d0946 100644
--- a/spectec/src/il/walk.ml
+++ b/spectec/src/il/walk.ml
@@ -35,7 +35,8 @@ type transformer = {
   transform_def_id: id -> id;
   transform_gram_id: id -> id;
 
-  filter_exp : exp -> exp option
+  (* Adjusting traversal *)
+  transform_types_of_exp : bool
 }
 
 let id = Fun.id
@@ -55,7 +56,7 @@ let base_transformer = {
   transform_def_id = id;
   transform_gram_id = id;
 
-  filter_exp = op_id
+  transform_types_of_exp = true
 }
 
 let rec transform_typ t typ = 
@@ -72,7 +73,6 @@ let rec transform_typ t typ =
 
 and transform_exp t e =
   let f = t.transform_exp in
-  let g = t.filter_exp in
   let t_exp = transform_exp t in
   let it =
     match e.it with
@@ -107,13 +107,8 @@ and transform_exp t e =
     | SubE (e1, _t1, t2) -> SubE (t_exp e1, _t1, t2)
     | IfE (e1, e2, e3) -> IfE (t_exp e1, t_exp e2, t_exp e3)
   in
-
-  let e' = 
-    match g {e with it; note = transform_typ t e.note } with 
-    | Some e' -> f e'
-    | None -> e 
-  in
-  f e'
+  let typ' = if t.transform_types_of_exp then transform_typ t e.note else e.note in 
+  f { e with it; note = typ' }
 
 and transform_iter t iter =
   match iter with
diff --git a/spectec/src/middlend/dune b/spectec/src/middlend/dune
index c2bc064072..31f3bb2553 100644
--- a/spectec/src/middlend/dune
+++ b/spectec/src/middlend/dune
@@ -15,5 +15,6 @@
     aliasDemut
     improveids
     ite
+    patSimp
   )
 )
diff --git a/spectec/src/middlend/patSimp.ml b/spectec/src/middlend/patSimp.ml
new file mode 100644
index 0000000000..cf9d0066a5
--- /dev/null
+++ b/spectec/src/middlend/patSimp.ml
@@ -0,0 +1,173 @@
+(* 
+  This pass simplifies definite iteration and non-linear patterns
+  by utilizing premises.
+  
+  It achieves this through the following steps:
+  - For non-linear patterns:
+    * For each clause, we traverse the arguments and keep track
+    of all variables in expressions. If a variable appears more
+    than once, we generate a fresh version of the variable and
+    keep it for later.
+    * Once we have traversed the entire argument list, we use
+    the variables tracked to generate new quantifiers and equality
+    premises.
+  - For definite iteration:
+    * For each clause, we traverse the arguments, and collect
+    all variables used for definite iteration (i.e. the e in ListN e _ )
+    and the respective lists being iterated.
+    * Using the collected variables, we iterate through the list to create
+    the equality premises.
+
+
+  For example (for non-linear pattern), take the function:
+
+  def $find(nat, nat* ) : bool
+  def $find(n, eps ) = false
+  def $find(n, n n'* ) = true
+  def $find(n, n_1 n'* ) = $find( n, n'* )
+  Would be transformed as such:
+
+  def $find(nat : nat, nat* ) : bool
+  def $find{n : nat}(n, []) = false
+  def $find{n : nat, `n'*` : nat*, n#1 : nat}(n, [n#1] ++ n'*{n' <- `n'*`}) = true
+    -- if (n = n#1)
+  def $find{n : nat, n_1 : nat, `n'*` : nat*}(n, [n_1] ++ n'*{n' <- `n'*`}) = $find(n, n'*{n' <- `n'*`})
+
+  For definite iteration:
+
+  def $len( int* ) : nat
+  def $len(i^n) = n 
+
+  to
+  
+  def $len(int* ) : nat
+  def $len{n : nat, `i*` : int*}(i*{i <- `i*`}) = n
+    -- if (n = |`i*`|)
+    
+NOTE: Currently does not work with dependent types. As such, it depends on the type family removal pass and undep pass.
+This is a todo for the future.
+*)
+
+open Il.Ast
+open Il.Walk
+open Util
+open Source
+
+module StringMap = Map.Make(String)
+
+let (let*) = Option.bind
+
+let create_eq_prem id typ id' = 
+  let idexp = VarE id $$ id.at % typ in
+  let idexp' = VarE (id' $ id.at) $$ id.at % typ in
+  let exp = CmpE (`EqOp, `BoolT, idexp, idexp') $$ id.at % (BoolT $ id.at) in
+  IfPr exp $ id.at
+
+let create_eq_prem_exp e e' = 
+  let exp = CmpE (`EqOp, `BoolT, e, e') $$ e.at % (BoolT $ e.at) in
+  IfPr exp $ e.at 
+
+let create_iter_prem scope base_prem = 
+  List.fold_left (fun prem iterexp -> 
+    IterPr (prem, iterexp) $ prem.at
+  ) base_prem scope
+
+let t_exp varmap exp = 
+  match exp.it with
+  | VarE id -> 
+    let fresh_var = ref id.it in 
+    varmap := StringMap.update id.it (fun opt -> 
+      match opt with
+      | Some lst -> 
+        fresh_var := Utils.generate_var (List.map fst (StringMap.bindings !varmap) @ lst) id.it;    
+        Some (!fresh_var :: lst)
+      | None -> Some []
+    ) !varmap;
+    { exp with it = VarE (!fresh_var $ id.at) }
+  | _ -> exp
+
+let rec c_exp scope exp = 
+  match exp.it with
+  | IterE (_, (ListN (e'', _), eps)) -> ([e'', eps, scope], true)
+  | IterE (e, (iter, eps)) ->
+    let lst_cl = base_collector [] (@) in
+    let cl = { lst_cl with collect_exp = c_exp ((iter, eps) :: scope) } in
+    let def_lst = collect_exp cl e in
+    (def_lst, false)
+  | _ -> ([], true)
+
+let t_exp2 exp = 
+  match exp.it with
+  | IterE (e, (ListN _, eps)) -> { exp with it = IterE (e, (List, eps)) }
+  | _ -> exp
+
+let t_typ2 typ = 
+  match typ.it with
+  | IterT (t, ListN _) -> { typ with it = IterT (t, List) }
+  | _ -> typ
+    
+let handle_non_linear clause = 
+  let DefD (quants, args, exp, prs) = clause.it in
+  let varmap = ref StringMap.empty in 
+  let tf = { base_transformer with transform_exp = t_exp varmap; transform_types_of_exp = false } in
+  let args' = List.map (transform_arg tf) args in 
+  let new_quants, new_prs = List.filter_map (fun q -> match q.it with
+    | ExpP (id, typ) -> 
+      let* ts = StringMap.find_opt id.it !varmap in
+      if ts = [] then None else 
+      let q' = List.map (fun id' -> ExpP (id' $ id.at, typ) $ id.at) ts in
+      let prs'= List.map (create_eq_prem id typ) ts in
+      Some (q', prs')
+    | _ -> None
+  ) quants |> List.split
+  in
+
+  { clause with it = DefD (quants @ (List.concat new_quants), args', exp, prs @ (List.concat new_prs)) }
+
+let handle_definite_iter clause = 
+  let DefD (quants, args, exp, prs) = clause.it in
+  let lst_cl = base_collector [] (@) in
+  let cl = { lst_cl with collect_exp = c_exp [] } in
+  let tf = { base_transformer with transform_exp = t_exp2; transform_typ = t_typ2 } in
+
+  let def_lst = List.concat_map (collect_arg cl) args in 
+  let new_prs = List.concat_map (fun (n, eps, scope) ->
+    let lene e = LenE e $$ e.at % (NumT `NatT $ e.at) in 
+    List.map (fun (_, e) -> 
+      let base_prem = create_eq_prem_exp n (lene e) in
+      create_iter_prem scope base_prem) eps   
+  ) def_lst 
+  in
+  
+  { clause with it = DefD (quants, List.map (transform_arg tf) args, exp, prs @ new_prs) }
+
+let handle_definite_iter_rel rule = 
+  let RuleD (id, quants, mixop, exp, prs) = rule.it in
+  let lst_cl = base_collector [] (@) in
+  let cl = { lst_cl with collect_exp = c_exp [] } in
+
+  let def_lst = collect_exp cl exp @ List.concat_map (collect_prem cl) prs in 
+  let def_lst_uniq = Lib.List.nub (fun (n1, eps1, _) (n2, eps2, _) ->
+    Il.Eq.eq_exp n1 n2 && List.length eps1 = List.length eps2 &&
+    List.for_all2 (fun (id1, e1) (id2, e2) -> id1.it = id2.it && Il.Eq.eq_exp e1 e2) eps1 eps2    
+  ) def_lst in
+  let new_prs = List.concat_map (fun (n, eps, scope) ->
+    let lene e = LenE e $$ e.at % (NumT `NatT $ e.at) in 
+    List.map (fun (_, e) -> 
+      let base_prem = create_eq_prem_exp n (lene e) in
+      create_iter_prem scope base_prem) eps   
+  ) def_lst_uniq
+  in
+  
+  { rule with it = RuleD (id, quants, mixop, exp, prs @ new_prs) }
+
+let rec t_def def = 
+  match def.it with
+  | DecD (id, params, rt, clauses) -> { def with it = DecD (id, params, rt, 
+    clauses |> List.map handle_definite_iter |> List.map (handle_non_linear)) }
+  | RelD (id, qs, mixop, typ, rules) -> 
+    { def with it = RelD (id, qs, mixop, typ, List.map handle_definite_iter_rel rules) }
+  | RecD defs -> { def with it = RecD (List.map t_def defs) }
+  | _ -> def
+
+let transform il = List.map t_def il
diff --git a/spectec/src/middlend/patSimp.mli b/spectec/src/middlend/patSimp.mli
new file mode 100644
index 0000000000..64d020ff9d
--- /dev/null
+++ b/spectec/src/middlend/patSimp.mli
@@ -0,0 +1 @@
+val transform : Il.Ast.script -> Il.Ast.script
\ No newline at end of file
diff --git a/spectec/test-middlend/test.spectec b/spectec/test-middlend/test.spectec
index 933b224916..82d8a46852 100644
--- a/spectec/test-middlend/test.spectec
+++ b/spectec/test-middlend/test.spectec
@@ -33,4 +33,27 @@ def $t_totalize3(n) = $($t_totalize(n) + $t_totalize2($(n + 10)))
 ;; def $t_totalize3(n) = $($t_totalize(n) + $t_totalize2($t_totalize(n)))
 ;;
 ;; def $t_totalize4(nat) : nat hint(partial)
-;; def $t_totalize4(n) = $t_totalize($t_totalize(n))
\ No newline at end of file
+;; def $t_totalize4(n) = $t_totalize($t_totalize(n))
+
+;;
+;;  Pattern Simp testing
+;;
+
+syntax A = B nat
+
+def $t_patsimp(nat, nat) : nat
+def $t_patsimp(n, n) = n
+def $t_patsimp(n, m) = $(n + m)
+
+def $t_patsimp2(nat, nat, A) : nat
+def $t_patsimp2(n, n, B n) = n
+def $t_patsimp2(n, m, B m) = $(n + m)
+def $t_patsimp2(n, m, B k) = $(n + m + k)
+
+def $find(nat, nat*) : bool
+def $find(n, eps) = false
+def $find(n, n n'*) = true
+def $find(n, n_1 n'*) = $find(n, n'*)
+
+def $len(int*) : nat
+def $len(i^n) = n 
\ No newline at end of file