Module red1 := ext_red_one e_invert.
Set Implicit Arguments.
Set Bullet Behavior "Strict Subproofs".

Lemma weaken_head_reduction : forall G0 a a',
head_reduction G0 a a' ->
forall E F G, (G0 = F ++ G) -> AnnCtx (F ++ E ++ G) -> head_reduction (F ++ E ++ G) a a'.