Section STABILITY.
Variable CS: compspecs.
Variables Delta Delta': tycontext.
Hypothesis extends: tycontext_sub Delta Delta'.

Lemma tc_expr_lvalue_sub: forall rho,
typecheck_environ Delta rho ->
forall e,
tc_expr Delta e rho |-- tc_expr Delta' e rho /\
tc_lvalue Delta e rho |-- tc_lvalue Delta' e rho.