WP on expressions

examples/hoare_logic/wp2/why3session.xml

 <?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE why3session SYSTEM "/home/marche/why3/share/why3session.dtd">
+<!DOCTYPE why3session SYSTEM "/usr/local/share/why3/why3session.dtd">
 <why3session
- name="hoare_logic/wp2/why3session.xml">
+ name="examples/hoare_logic/wp2/why3session.xml">
  <prover
   id="0"
   name="Alt-Ergo"
@@ -29,16 +29,16 @@
  <file
   name="../wp2.mlw"
   verified="true"
-  expanded="false">
+  expanded="true">
   <theory
    name="Imp"
-   locfile="hoare_logic/wp2/../wp2.mlw"
+   locfile="examples/hoare_logic/wp2/../wp2.mlw"
    loclnum="6" loccnumb="7" loccnume="10"
    verified="true"
-   expanded="false">
+   expanded="true">
    <goal
     name="eval_subst_term"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="99" loccnumb="6" loccnume="21"
     sum="57686028d06a25fd21f0d145ae3c39cc"
     proved="true"
@@ -56,7 +56,7 @@
    </goal>
    <goal
     name="eval_term_change_free"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="105" loccnumb="6" loccnume="27"
     sum="bc8ecc8fa47f6b0378862b9ff6c140b4"
     proved="true"
@@ -74,7 +74,7 @@
    </goal>
    <goal
     name="eval_subst"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="131" loccnumb="6" loccnume="16"
     sum="e7187a74f15a81f5d32beb4c7e17ebd5"
     proved="true"
@@ -92,7 +92,7 @@
    </goal>
    <goal
     name="eval_swap"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="137" loccnumb="6" loccnume="15"
     sum="df0a3794f91d81e47b10e6e3cbb7ffd5"
     proved="true"
@@ -117,7 +117,7 @@
    </goal>
    <goal
     name="eval_change_free"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="143" loccnumb="6" loccnume="22"
     sum="d5dd6566baac671168e7b098cdc7b9d5"
     proved="true"
@@ -135,7 +135,7 @@
    </goal>
    <goal
     name="check_skip"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="158" loccnumb="6" loccnume="16"
     sum="d0110d5cf0e45b1a226959c69106f31e"
     proved="true"
@@ -184,7 +184,7 @@
    </goal>
    <goal
     name="steps_non_neg"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="227" loccnumb="6" loccnume="19"
     sum="6192ae6d220dcba9ed5131230fef77d7"
     proved="true"
@@ -202,11 +202,11 @@
    </goal>
    <goal
     name="many_steps_seq"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="231" loccnumb="6" loccnume="20"
     sum="701bc2e3c241588769058c0765a02a42"
     proved="true"
-    expanded="false"
+    expanded="true"
     shape="ainfix =V6ainfix +ainfix +c1V9V10Aamany_stepsV7V8V5V2V3aSskipV10Aamany_stepsV0V1V4V7V8aSskipV9EIamany_stepsV0V1aSseqV4V5V2V3aSskipV6F">
     <proof
      prover="3"
@@ -221,13 +221,13 @@
   </theory>
   <theory
    name="TestSemantics"
-   locfile="hoare_logic/wp2/../wp2.mlw"
+   locfile="examples/hoare_logic/wp2/../wp2.mlw"
    loclnum="262" loccnumb="7" loccnume="20"
    verified="true"
    expanded="false">
    <goal
     name="Test13"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="269" loccnumb="5" loccnume="11"
     sum="5a2b877c54aa3fb4478e1df947c07a82"
     proved="true"
@@ -260,7 +260,7 @@
    </goal>
    <goal
     name="Test42"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="272" loccnumb="5" loccnume="11"
     sum="26b202b461b9dc6aa38c7c2b25add03f"
     proved="true"
@@ -293,7 +293,7 @@
    </goal>
    <goal
     name="Test0"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="275" loccnumb="5" loccnume="10"
     sum="d1efb52f7259cb2f1b22f16b0a97ea9c"
     proved="true"
@@ -326,7 +326,7 @@
    </goal>
    <goal
     name="Test55"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="278" loccnumb="5" loccnume="11"
     sum="7c6ef63d0bb6a469fe0d5b3879f63c4f"
     proved="true"
@@ -344,7 +344,7 @@
    </goal>
    <goal
     name="Ass42"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="281" loccnumb="5" loccnume="10"
     sum="31aeebca6b452917821f32f389b506bb"
     proved="true"
@@ -377,7 +377,7 @@
    </goal>
    <goal
     name="If42"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="287" loccnumb="5" loccnume="9"
     sum="bbc444c8bd41e9036d9ec951e0a915a1"
     proved="true"
@@ -396,17 +396,17 @@
   </theory>
   <theory
    name="HoareLogic"
-   locfile="hoare_logic/wp2/../wp2.mlw"
+   locfile="examples/hoare_logic/wp2/../wp2.mlw"
    loclnum="302" loccnumb="7" loccnume="17"
    verified="true"
-   expanded="false">
+   expanded="true">
    <goal
     name="consequence_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="309" loccnumb="6" loccnume="22"
     sum="c1f5595ddd954b6361531a9cb635279b"
     proved="true"
-    expanded="false"
+    expanded="true"
     shape="avalid_tripleV1V4V3Iavalid_fmlaaFimpliesV2V3Iavalid_tripleV0V4V2Iavalid_fmlaaFimpliesV1V0F">
     <proof
      prover="4"
@@ -427,7 +427,7 @@
    </goal>
    <goal
     name="skip_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="316" loccnumb="6" loccnume="15"
     sum="73e47f5d6901d2f852f0c089cfe9027d"
     proved="true"
@@ -445,7 +445,7 @@
    </goal>
    <goal
     name="assign_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="319" loccnumb="6" loccnume="17"
     sum="5ad7f36cb5982497693bbd3917b38dd5"
     proved="true"
@@ -463,7 +463,7 @@
    </goal>
    <goal
     name="seq_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="324" loccnumb="6" loccnume="14"
     sum="1a26088dc2dd29482c5092b6ac4ff809"
     proved="true"
@@ -488,7 +488,7 @@
    </goal>
    <goal
     name="if_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="329" loccnumb="6" loccnume="13"
     sum="3bebb0334fdf15d6238553f897994e1d"
     proved="true"
@@ -506,7 +506,7 @@
    </goal>
    <goal
     name="assert_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="335" loccnumb="6" loccnume="17"
     sum="b11afd1baac4615f908daadec96d093c"
     proved="true"
@@ -524,7 +524,7 @@
    </goal>
    <goal
     name="assert_rule_ext"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="339" loccnumb="6" loccnume="21"
     sum="189817af6b3e698754f066618e6681a5"
     proved="true"
@@ -542,7 +542,7 @@
    </goal>
    <goal
     name="while_rule"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="343" loccnumb="6" loccnume="16"
     sum="a1136f47e552feb3c79f635b836bda93"
     proved="true"
@@ -560,7 +560,7 @@
    </goal>
    <goal
     name="while_rule_ext"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="348" loccnumb="6" loccnume="20"
     sum="2b6ff464c6bc40e843b0c4d2e7536e09"
     proved="true"
@@ -579,13 +579,13 @@
   </theory>
   <theory
    name="WP WP"
-   locfile="hoare_logic/wp2/../wp2.mlw"
+   locfile="examples/hoare_logic/wp2/../wp2.mlw"
    loclnum="360" loccnumb="7" loccnume="9"
    verified="true"
    expanded="false">
    <goal
     name="assigns_refl"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="370" loccnumb="6" loccnume="18"
     sum="06b520020b55dcb7f4935d3d5c8e821a"
     proved="true"
@@ -602,7 +602,7 @@
    </goal>
    <goal
     name="assigns_trans"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="373" loccnumb="6" loccnume="19"
     sum="faf97b15d0c4bb4b055b5bf87b56bcac"
     proved="true"
@@ -619,7 +619,7 @@
    </goal>
    <goal
     name="assigns_union_left"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="378" loccnumb="6" loccnume="24"
     sum="66e032a193a387c492501dc3846056cb"
     proved="true"
@@ -636,7 +636,7 @@
    </goal>
    <goal
     name="assigns_union_right"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="382" loccnumb="6" loccnume="25"
     sum="1ed0b8be1cdffeff0d3796c96087a84d"
     proved="true"
@@ -653,7 +653,7 @@
    </goal>
    <goal
     name="WP_parameter compute_writes"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="396" loccnumb="10" loccnume="24"
     expl="parameter compute_writes"
     sum="e1ad5edc34873eaa959f2469771f12b7"
@@ -665,10 +665,10 @@
     <transf
      name="split_goal"
      proved="true"
-     expanded="true">
+     expanded="false">
      <goal
       name="WP_parameter compute_writes.1"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="a531cd444b99055eef6fcad0ffae99ea"
@@ -688,7 +688,7 @@
      </goal>
      <goal
       name="WP_parameter compute_writes.2"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="7ad586ff4b17b7097a64232ad0e619f3"
@@ -709,7 +709,7 @@
      </goal>
      <goal
       name="WP_parameter compute_writes.3"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="1965fac020be25adfc5d4a8de7cd05d7"
@@ -737,7 +737,7 @@
      </goal>
      <goal
       name="WP_parameter compute_writes.4"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="58552f908345b33a9a5dd914446ddcfb"
@@ -758,7 +758,7 @@
      </goal>
      <goal
       name="WP_parameter compute_writes.5"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="f29d8147b569ed2a9a09989b7a3d8f40"
@@ -779,7 +779,7 @@
      </goal>
      <goal
       name="WP_parameter compute_writes.6"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="396" loccnumb="10" loccnume="24"
       expl="parameter compute_writes"
       sum="8692a4caadb055588117f3c66a461995"
@@ -802,7 +802,7 @@
    </goal>
    <goal
     name="WP_parameter wp"
-    locfile="hoare_logic/wp2/../wp2.mlw"
+    locfile="examples/hoare_logic/wp2/../wp2.mlw"
     loclnum="432" loccnumb="10" loccnume="12"
     expl="parameter wp"
     sum="1c4c1bb9c160304e6e0411df18a765b0"
@@ -814,10 +814,10 @@
     <transf
      name="split_goal"
      proved="true"
-     expanded="true">
+     expanded="false">
      <goal
       name="WP_parameter wp.1"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="d3ca27059c5ec4c3a2403391d70c3d77"
@@ -869,7 +869,7 @@
      </goal>
      <goal
       name="WP_parameter wp.2"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="6910613be73da88fefc0e98306dc6a78"
@@ -921,7 +921,7 @@
      </goal>
      <goal
       name="WP_parameter wp.3"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="8f814b54733daa2438b60bae70bdc325"
@@ -973,7 +973,7 @@
      </goal>
      <goal
       name="WP_parameter wp.4"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="cdd6ff3e6b9b0147ba69efeb36077964"
@@ -994,7 +994,7 @@
      </goal>
      <goal
       name="WP_parameter wp.5"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="6eac56dea71edb9e615f1d5ae6644293"
@@ -1046,7 +1046,7 @@
      </goal>
      <goal
       name="WP_parameter wp.6"
-      locfile="hoare_logic/wp2/../wp2.mlw"
+      locfile="examples/hoare_logic/wp2/../wp2.mlw"
       loclnum="432" loccnumb="10" loccnume="12"
       expl="parameter wp"
       sum="a445cc5a717592ffc477eb84413d83e4"

examples/hoare_logic/wp3.mlw

+
+(** {1 A certified WP calculus} *)
+
+(** {2 A simple imperative language with expressions, syntax and semantics} *)
+
+theory ImpExpr
+
+use import int.Int
+use import bool.Bool
+
+(** types and values *)
+
+type datatype = TYunit | TYint | TYbool
+type value = Vvoid | Vint int | Vbool bool
+
+(** terms and formulas *)
+
+type operator = Oplus | Ominus | Omult | Ole
+
+type ident = int
+
+constant result : ident = (-1)
+
+type term =
+  | Tvalue value
+  | Tvar ident
+  | Tderef ident
+  | Tbin term operator term
+
+type fmla =
+  | Fterm term
+  | Fand fmla fmla
+  | Fnot fmla
+  | Fimplies fmla fmla
+  | Flet ident term fmla
+  | Fforall ident datatype fmla
+
+use map.Map as IdMap
+type env = IdMap.map ident value
+
+(** semantics of formulas *)
+
+function eval_bin (x:value) (op:operator) (y:value) : value =
+  match x,y with
+  | Vint x,Vint y ->
+     match op with
+     | Oplus -> Vint (x+y)
+     | Ominus -> Vint (x-y)
+     | Omult -> Vint (x*y)
+     | Ole -> Vbool (if x <= y then True else False)
+     end
+  | _,_ -> Vbool False
+  end
+
+function get_env (i:ident) (e:env) : value = IdMap.get e i
+
+function eval_term (sigma:env) (pi:env) (t:term) : value =
+  match t with
+  | Tvalue v -> v
+  | Tvar id -> get_env id pi
+  | Tderef id -> get_env id sigma
+  | Tbin t1 op t2 ->
+     eval_bin (eval_term sigma pi t1) op (eval_term sigma pi t2)
+  end
+
+predicate eval_fmla (sigma:env) (pi:env) (f:fmla) =
+  match f with
+  | Fterm t -> eval_term sigma pi t = Vbool True
+  | Fand f1 f2 -> eval_fmla sigma pi f1 /\ eval_fmla sigma pi f2
+  | Fnot f -> not (eval_fmla sigma pi f)
+  | Fimplies f1 f2 -> eval_fmla sigma pi f1 -> eval_fmla sigma pi f2
+  | Flet x t f ->
+      eval_fmla sigma (IdMap.set pi x (eval_term sigma pi t)) f
+  | Fforall x TYint f ->
+     forall n:int. eval_fmla sigma (IdMap.set pi x (Vint n)) f
+  | Fforall x TYbool f ->
+     forall b:bool.
+        eval_fmla sigma (IdMap.set pi x (Vbool b)) f
+  | Fforall x TYunit f ->
+        eval_fmla sigma (IdMap.set pi x Vvoid) f
+  end
+
+(** substitution of a reference [r] by a logic variable [v]
+   warning: proper behavior only guaranted if [v] is fresh *)
+
+function subst_term (e:term) (r:ident) (v:ident) : term =
+  match e with
+  | Tvalue _ | Tvar _ -> e
+  | Tderef x -> if r=x then Tvar v else e
+  | Tbin e1 op e2 -> Tbin (subst_term e1 r v) op (subst_term e2 r v)
+  end
+
+predicate fresh_in_term (id:ident) (t:term) =
+  match t with
+  | Tvalue _ -> true
+  | Tvar v -> id <> v
+  | Tderef _ -> true
+  | Tbin t1 _ t2 -> fresh_in_term id t1 /\ fresh_in_term id t2
+  end
+
+lemma eval_subst_term:
+  forall sigma pi:env, e:term, x:ident, v:ident.
+    fresh_in_term v e ->
+    eval_term sigma pi (subst_term e x v) =
+    eval_term (IdMap.set sigma x (IdMap.get pi v)) pi e
+
+lemma eval_term_change_free :
+  forall t:term, sigma pi:env, id:ident, v:value.
+    fresh_in_term id t ->
+    eval_term sigma (IdMap.set pi id v) t = eval_term sigma pi t
+
+predicate fresh_in_fmla (id:ident) (f:fmla) =
+  match f with
+  | Fterm e -> fresh_in_term id e
+  | Fand f1 f2   | Fimplies f1 f2 ->
+      fresh_in_fmla id f1 /\ fresh_in_fmla id f2
+  | Fnot f -> fresh_in_fmla id f
+  | Flet y t f -> id <> y /\ fresh_in_term id t /\ fresh_in_fmla id f
+  | Fforall y ty f -> id <> y /\ fresh_in_fmla id f
+  end
+
+function subst (f:fmla) (x:ident) (v:ident) : fmla =
+  match f with
+  | Fterm e -> Fterm (subst_term e x v)
+  | Fand f1 f2 -> Fand (subst f1 x v) (subst f2 x v)
+  | Fnot f -> Fnot (subst f x v)
+  | Fimplies f1 f2 -> Fimplies (subst f1 x v) (subst f2 x v)
+  | Flet y t f -> Flet y (subst_term t x v) (subst f x v)
+  | Fforall y ty f -> Fforall y ty (subst f x v)
+  end
+
+
+lemma eval_subst:
+  forall f:fmla, sigma pi:env, x:ident, v:ident.
+    fresh_in_fmla v f ->
+    (eval_fmla sigma pi (subst f x v) <->
+     eval_fmla (IdMap.set sigma x (IdMap.get pi v)) pi f)
+
+lemma eval_swap:
+  forall f:fmla, sigma pi:env, id1 id2:ident, v1 v2:value.
+    id1 <> id2 ->
+    (eval_fmla sigma (IdMap.set (IdMap.set pi id1 v1) id2 v2) f <->
+    eval_fmla sigma (IdMap.set (IdMap.set pi id2 v2) id1 v1) f)
+
+lemma eval_change_free :
+  forall f:fmla, sigma pi:env, id:ident, v:value.
+    fresh_in_fmla id f ->
+    (eval_fmla sigma (IdMap.set pi id v) f <-> eval_fmla sigma pi f)
+
+(* expressions *)
+
+type expr =
+  | Evalue value
+  | Ebin expr operator expr
+  | Evar ident
+  | Ederef ident
+  | Eassign ident expr
+  | Eseq expr expr
+  | Elet ident expr expr
+  | Eif expr expr expr
+  | Eassert fmla
+  | Ewhile expr fmla expr
+
+constant void : expr = Evalue Vvoid
+
+(*
+lemma check_skip:
+  forall s:stmt. s=Sskip \/s<>Sskip
+*)
+
+(** small-steps semantics for statements *)
+
+inductive one_step env env expr env env expr =
+
+  | one_step_assign_ctxt:
+      forall sigma pi sigma' pi':env, x:ident, e e':expr.
+        one_step sigma pi e sigma' pi' e' ->
+        one_step sigma pi (Eassign x e)
+                 sigma' pi' (Eassign x e')
+
+  | one_step_assign_value:
+      forall sigma pi:env, x:ident, v:value, e:term.
+        one_step sigma pi (Eassign x (Evalue v))
+                 (IdMap.set sigma x v) pi void
+
+  | one_step_seq_ctxt:
+      forall sigma pi sigma' pi':env, e1 e1' e2:expr.
+        one_step sigma pi e1 sigma' pi' e1' ->
+          one_step sigma pi (Eseq e1 e2) sigma' pi' (Eseq e1' e2)
+
+  | one_step_seq_value:
+      forall sigma pi:env, id:ident, e:expr.
+        one_step sigma pi (Eseq void e) sigma pi e
+
+  | one_step_let_ctxt:
+      forall sigma pi sigma' pi':env, id:ident, e1 e1' e2:expr.
+        one_step sigma pi e1 sigma' pi' e1' ->
+          one_step sigma pi (Elet id e1 e2) sigma' pi' (Elet id e1' e2)
+
+  | one_step_let_value:
+      forall sigma pi:env, id:ident, v:value, e:expr.
+        one_step sigma pi (Elet id (Evalue v) e) sigma (IdMap.set pi id v) e
+
+  | one_step_if_ctxt:
+      forall sigma pi sigma' pi':env, id:ident, e1 e1' e2 e3:expr.
+        one_step sigma pi e1 sigma' pi' e1' ->
+          one_step sigma pi (Eif e1 e2 e3) sigma' pi' (Eif e1' e2 e3)
+
+  | one_step_if_true:
+      forall sigma pi:env, e:term, e1 e2:expr.
+        one_step sigma pi (Eif (Evalue (Vbool True)) e1 e2) sigma pi e1
+
+  | one_step_if_false:
+      forall sigma pi:env, e:term, e1 e2:expr.
+        one_step sigma pi (Eif (Evalue (Vbool False)) e1 e2) sigma pi e2
+
+  | one_step_assert:
+      forall sigma pi:env, f:fmla.
+        eval_fmla sigma pi f ->
+          one_step sigma pi (Eassert f) sigma pi void
+
+  | one_step_while:
+      forall sigma pi:env, e:expr, inv:fmla, e':expr.
+        one_step sigma pi (Ewhile e inv e') sigma pi 
+        (Eif e (Eseq e' (Ewhile e inv e')) void)
+
+(***
+
+  lemma progress:
+    forall s:state, i:expr.
+      i <> Sskip ->
+      exists s':state, i':expr. one_step s i s' i'
+
+*)
+
+ (** many steps of execution *)
+
+ inductive many_steps env env expr env env expr int =
+   | many_steps_refl:
+     forall sigma pi:env, i:expr. many_steps sigma pi i sigma pi i 0