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-rw-r--r--kernel/esubst.ml10
-rw-r--r--kernel/esubst.mli6
2 files changed, 11 insertions, 5 deletions
diff --git a/kernel/esubst.ml b/kernel/esubst.ml
index a11a0dc00..91cc64523 100644
--- a/kernel/esubst.ml
+++ b/kernel/esubst.ml
@@ -19,6 +19,8 @@ open Util
(*********************)
(* Explicit lifts and basic operations *)
+(* Invariant to preserve in this module: no lift contains two consecutive
+ [ELSHFT] nor two consecutive [ELLFT]. *)
type lift =
| ELID
| ELSHFT of lift * int (* ELSHFT(l,n) == lift of n, then apply lift l *)
@@ -28,15 +30,15 @@ type lift =
let el_id = ELID
(* compose a relocation of magnitude n *)
-let rec el_shft_rec n = function
- | ELSHFT(el,k) -> el_shft_rec (k+n) el
+let el_shft_rec n = function
+ | ELSHFT(el,k) -> ELSHFT(el,k+n)
| el -> ELSHFT(el,n)
let el_shft n el = if Int.equal n 0 then el else el_shft_rec n el
(* cross n binders *)
-let rec el_liftn_rec n = function
+let el_liftn_rec n = function
| ELID -> ELID
- | ELLFT(k,el) -> el_liftn_rec (n+k) el
+ | ELLFT(k,el) -> ELLFT(n+k, el)
| el -> ELLFT(n, el)
let el_liftn n el = if Int.equal n 0 then el else el_liftn_rec n el
diff --git a/kernel/esubst.mli b/kernel/esubst.mli
index b82d6fdf0..a674c425a 100644
--- a/kernel/esubst.mli
+++ b/kernel/esubst.mli
@@ -56,7 +56,11 @@ val comp : ('a subs * 'a -> 'a) -> 'a subs -> 'a subs -> 'a subs
(** {6 Compact representation } *)
(** Compact representation of explicit relocations
- [ELSHFT(l,n)] == lift of [n], then apply [lift l].
- - [ELLFT(n,l)] == apply [l] to de Bruijn > [n] i.e under n binders. *)
+ - [ELLFT(n,l)] == apply [l] to de Bruijn > [n] i.e under n binders.
+
+ Invariant ensured by the private flag: no lift contains two consecutive
+ [ELSHFT] nor two consecutive [ELLFT].
+*)
type lift = private
| ELID
| ELSHFT of lift * int