diff --git a/sledge/src/fol.ml b/sledge/src/fol.ml
index 168a230f6..f1c322f77 100644
--- a/sledge/src/fol.ml
+++ b/sledge/src/fol.ml
@@ -103,7 +103,9 @@ and Trm : sig
   val _Record : trm array -> trm
   val _Ancestor : int -> trm
   val _Apply : Funsym.t -> trm array -> trm
+  val add : trm -> trm -> trm
   val sub : trm -> trm -> trm
+  val seq_size_exn : trm -> trm
 end = struct
   type var = Var.t
 
@@ -186,6 +188,8 @@ end = struct
                 elts )
         elts]
 
+  let pp = ppx (fun _ -> None)
+
   let invariant e =
     let@ () = Invariant.invariant [%here] e [%sexp_of: trm] in
     match e with
@@ -224,11 +228,132 @@ end = struct
     | Compound -> Arith a )
     |> check invariant
 
+  let add x y = _Arith Arith.(add (trm x) (trm y))
   let sub x y = _Arith Arith.(sub (trm x) (trm y))
   let _Splat x = Splat x |> check invariant
-  let _Sized seq siz = Sized {seq; siz} |> check invariant
-  let _Extract seq off len = Extract {seq; off; len} |> check invariant
-  let _Concat es = Concat es |> check invariant
+
+  let seq_size_exn =
+    let invalid = Invalid_argument "seq_size_exn" in
+    let rec seq_size_exn = function
+      | Sized {siz= n} | Extract {len= n} -> n
+      | Concat a0U ->
+          Array.fold ~f:(fun aJ a0I -> add a0I (seq_size_exn aJ)) a0U zero
+      | _ -> raise invalid
+    in
+    seq_size_exn
+
+  let seq_size e =
+    try Some (seq_size_exn e) with Invalid_argument _ -> None
+
+  let _Sized seq siz =
+    ( match seq_size seq with
+    (* ⟨n,α⟩ ==> α when n ≡ |α| *)
+    | Some n when equal_trm siz n -> seq
+    | _ -> Sized {seq; siz} )
+    |> check invariant
+
+  let partial_compare x y =
+    match sub x y with
+    | Z z -> Some (Int.sign (Z.sign z))
+    | Q q -> Some (Int.sign (Q.sign q))
+    | _ -> None
+
+  let partial_ge x y =
+    match partial_compare x y with Some (Pos | Zero) -> true | _ -> false
+
+  let empty_seq = Concat [||]
+
+  let rec _Extract seq off len =
+    [%trace]
+      ~call:(fun {pf} -> pf "%a" pp (Extract {seq; off; len}))
+      ~retn:(fun {pf} -> pf "%a" pp)
+    @@ fun () ->
+    (* _[_,0) ==> ⟨⟩ *)
+    ( if equal_trm len zero then empty_seq
+    else
+      let o_l = add off len in
+      match seq with
+      (* α[m,k)[o,l) ==> α[m+o,l) when k ≥ o+l *)
+      | Extract {seq= a; off= m; len= k} when partial_ge k o_l ->
+          _Extract a (add m off) len
+      (* ⟨n,E^⟩[o,l) ==> ⟨l,E^⟩ when n ≥ o+l *)
+      | Sized {siz= n; seq= Splat _ as e} when partial_ge n o_l ->
+          _Sized e len
+      (* ⟨n,a⟩[0,n) ==> ⟨n,a⟩ *)
+      | Sized {siz= n} when equal_trm off zero && equal_trm n len -> seq
+      (* For (α₀^α₁)[o,l) there are 3 cases:
+       *
+       * ⟨...⟩^⟨...⟩
+       *  [,)
+       * o < o+l ≤ |α₀| : (α₀^α₁)[o,l) ==> α₀[o,l) ^ α₁[0,0)
+       *
+       * ⟨...⟩^⟨...⟩
+       *   [  ,  )
+       * o ≤ |α₀| < o+l : (α₀^α₁)[o,l) ==> α₀[o,|α₀|-o) ^ α₁[0,l-(|α₀|-o))
+       *
+       * ⟨...⟩^⟨...⟩
+       *        [,)
+       * |α₀| ≤ o : (α₀^α₁)[o,l) ==> α₀[o,0) ^ α₁[o-|α₀|,l)
+       *
+       * So in general:
+       *
+       * (α₀^α₁)[o,l) ==> α₀[o,l₀) ^ α₁[o₁,l-l₀)
+       * where l₀ = max 0 (min l |α₀|-o)
+       *       o₁ = max 0 o-|α₀|
+       *)
+      | Concat na1N -> (
+        match len with
+        | Z l ->
+            Array.fold_map_until na1N (l, off)
+              ~f:(fun naI (l, oI) ->
+                if Z.equal Z.zero l then
+                  `Continue (_Extract naI oI zero, (l, oI))
+                else
+                  let nI = seq_size_exn naI in
+                  let oI_nI = sub oI nI in
+                  match oI_nI with
+                  | Z z ->
+                      let oJ = if Z.sign z <= 0 then zero else oI_nI in
+                      let lI = Z.(max zero (min l (neg z))) in
+                      let l = Z.(l - lI) in
+                      `Continue (_Extract naI oI (_Z lI), (l, oJ))
+                  | _ -> `Stop (Extract {seq; off; len}) )
+              ~finish:(fun (e1N, _) -> _Concat e1N)
+        | _ -> Extract {seq; off; len} )
+      (* α[o,l) *)
+      | _ -> Extract {seq; off; len} )
+    |> check invariant
+
+  and _Concat xs =
+    [%trace]
+      ~call:(fun {pf} -> pf "%a" pp (Concat xs))
+      ~retn:(fun {pf} -> pf "%a" pp)
+    @@ fun () ->
+    (* (α^(β^γ)^δ) ==> (α^β^γ^δ) *)
+    let flatten xs =
+      if Array.exists ~f:(function Concat _ -> true | _ -> false) xs then
+        Array.flat_map ~f:(function Concat s -> s | e -> [|e|]) xs
+      else xs
+    in
+    let simp_adjacent e f =
+      match (e, f) with
+      (* ⟨n,a⟩[o,k)^⟨n,a⟩[o+k,l) ==> ⟨n,a⟩[o,k+l) when n ≥ o+k+l *)
+      | ( Extract {seq= Sized {siz= n} as na; off= o; len= k}
+        , Extract {seq= na'; off= o_k; len= l} )
+        when equal_trm na na'
+             && equal_trm o_k (add o k)
+             && partial_ge n (add o_k l) ->
+          Some (_Extract na o (add k l))
+      (* ⟨m,E^⟩^⟨n,E^⟩ ==> ⟨m+n,E^⟩ *)
+      | Sized {siz= m; seq= Splat _ as a}, Sized {siz= n; seq= a'}
+        when equal_trm a a' ->
+          Some (_Sized a (add m n))
+      | _ -> None
+    in
+    let xs = flatten xs in
+    let xs = Array.reduce_adjacent ~f:simp_adjacent xs in
+    (if Array.length xs = 1 then xs.(0) else Concat xs) |> check invariant
+
   let _Select idx rcd = Select {idx; rcd} |> check invariant
   let _Update idx rcd elt = Update {idx; rcd; elt} |> check invariant
   let _Record es = Record es |> check invariant
@@ -275,15 +400,54 @@ module Fml = struct
     if x == zero then _Eq0 y
     else if y == zero then _Eq0 x
     else
+      let sort_eq x y =
+        match Sign.of_int (compare_trm x y) with
+        | Neg -> _Eq x y
+        | Zero -> tt
+        | Pos -> _Eq y x
+      in
       match (x, y) with
       (* x = y ==> 0 = x - y when x = y is an arithmetic equality *)
       | (Z _ | Q _ | Arith _), _ | _, (Z _ | Q _ | Arith _) ->
           _Eq0 (sub x y)
-      | _ -> (
-        match Sign.of_int (compare_trm x y) with
-        | Neg -> _Eq x y
-        | Zero -> tt
-        | Pos -> _Eq y x )
+      (* α^β^δ = α^γ^δ ==> β = γ *)
+      | Concat a, Concat b ->
+          let m = Array.length a in
+          let n = Array.length b in
+          let l = min m n in
+          let length_common_prefix =
+            let rec find_lcp i =
+              if i < l && equal_trm a.(i) b.(i) then find_lcp (i + 1) else i
+            in
+            find_lcp 0
+          in
+          if length_common_prefix = l then tt
+          else
+            let length_common_suffix =
+              let rec find_lcs i =
+                if equal_trm a.(m - 1 - i) b.(n - 1 - i) then
+                  find_lcs (i + 1)
+                else i
+              in
+              find_lcs 0
+            in
+            let length_common =
+              length_common_prefix + length_common_suffix
+            in
+            if length_common = 0 then sort_eq x y
+            else
+              let pos = length_common_prefix in
+              let a = Array.sub ~pos ~len:(m - length_common) a in
+              let b = Array.sub ~pos ~len:(n - length_common) b in
+              _Eq (_Concat a) (_Concat b)
+      | (Sized _ | Extract _ | Concat _), (Sized _ | Extract _ | Concat _)
+        ->
+          sort_eq x y
+      (* x = α ==> ⟨x,|α|⟩ = α *)
+      | x, ((Sized _ | Extract _ | Concat _) as a)
+       |((Sized _ | Extract _ | Concat _) as a), x ->
+          _Eq (_Sized x (seq_size_exn a)) a
+      | _ -> sort_eq x y
 end
 
 module Fmls = Prop.Fmls
@@ -662,7 +826,7 @@ module Term = struct
   let integer z = `Trm (_Z z)
   let rational q = `Trm (_Q q)
   let neg = ap1t @@ fun x -> _Arith Arith.(neg (trm x))
-  let add = ap2t @@ fun x y -> _Arith Arith.(add (trm x) (trm y))
+  let add = ap2t Trm.add
   let sub = ap2t Trm.sub
   let mulq q = ap1t @@ fun x -> _Arith Arith.(mulc q (trm x))
   let mul = ap2t @@ fun x y -> _Arith (Arith.mul x y)