Proof (proj2 (proj2 (proj2 (proj2 bigstep_to_steps)))).
Fixpoint esize (a: expr) : nat :=
match a with
| Eloc _ _ _ => 1%nat
| Evar _ _ => 1%nat
| Ederef r1 _ => S(esize r1)
| Efield l1 _ _ => S(esize l1)
| Eval _ _ => O
| Evalof l1 _ => S(esize l1)
| Eaddrof l1 _ => S(esize l1)
| Eunop _ r1 _ => S(esize r1)
| Ebinop _ r1 r2 _ => S(esize r1 + esize r2)%nat
| Ecast r1 _ => S(esize r1)
| Eseqand r1 r2 _ => S(esize r1)
| Eseqor r1 r2 _ => S(esize r1)
| Econdition r1 _ _ _ => S(esize r1)
| Esizeof _ _ => 1%nat
| Ealignof _ _ => 1%nat
| Eassign l1 r2 _ => S(esize l1 + esize r2)%nat
| Eassignop _ l1 r2 _ _ => S(esize l1 + esize r2)%nat
| Epostincr _ l1 _ => S(esize l1)
| Ecomma r1 r2 _ => S(esize r1 + esize r2)%nat
| Ecall r1 rl2 _ => S(esize r1 + esizelist rl2)%nat
| Ebuiltin ef tyargs rl _ => S(esizelist rl)
| Eparen r1 _ _ => S(esize r1)
end
with esizelist (el: exprlist) : nat :=
match el with
| Enil => O
| Econs r1 rl2 => S(esize r1 + esizelist rl2)%nat
end.

Lemma leftcontext_size:
forall from to C,
leftcontext from to C ->
forall e1 e2,
(esize e1 < esize e2)%nat ->
(esize (C e1) < esize (C e2))%nat
with leftcontextlist_size:
forall from C,
leftcontextlist from C ->
forall e1 e2,
(esize e1 < esize e2)%nat ->
(esizelist (C e1) < esizelist (C e2))%nat.