Section UnpackStratifiedSemanticsWithSeparation.
Context
{W V G S' U F world_erase VU GF A projA H HG}
`{SSS : StratifiedSemanticsWithSeparation W V G S' U F world_erase VU GF A projA H HG}.

Lemma sep_expr_safety : forall e e' w b1,
expr_erase HG e e'
-> exprEval H e (projA w) b1
-> exists b2, exprEval G e' w b2.