Add small docstring to subdiv checker

coq/SubdivsChecker.v

@@ -610,7 +610,12 @@ Definition checkPreconds (subdivs: list precond) (P: precond) :=
   let Piv := FloverMap.elements (fst P) in
   let Ps := map (fun P => FloverMap.elements (fst P)) subdivs in
   let S_qs := map snd subdivs in
-  covers Piv (sort Ps) && forallbTailrec (fun q => SMTLogic_eqb q (snd P)) S_qs.
+  (* Check that join of the preconditions for the subdivisions
+     covers the global precondition *)
+  covers Piv (sort Ps) &&
+         (* Check that additional constraints encoded by Daisy agree
+            for each subdivision *)
+         forallbTailrec (fun q => SMTLogic_eqb q (snd P)) S_qs.
 
 Lemma checkPreconds_sound (subdivs: list precond) E P :
   checkPreconds subdivs P = true ->
@@ -703,7 +708,7 @@ Proof.
   { apply unsat_qs. apply in_map_iff. now exists (P1, A, Qmap). }
   repeat split; eauto using resultLeq_range_sound, resultLeq_error_sound.
 Qed.
-  
+
 (*
   exists Gamma; intros approxE1E2.
   assert (approxEnv E1 (toRExpMap Gamma) A (freeVars e) NatSet.empty E2) as approxE1E2'