Section HENKIN.
#[local] Infix "=~=" := is_similar_to : type_scope.
Context {L : language}.
#[local] Notation L' := (augmented_language L Henkin_constants).
#[local] Notation hatom := (ivar + Henkin_constants)%type.
#[local] Notation hsubst := (hatom -> trm L').
#[local] Existing Instance constant_symbols_sim.
#[local] Existing Instance trm_sim.
#[local] Existing Instance trms_sim.
#[local] Existing Instance frm_sim.
#[local] Existing Instance frms_sim.

Lemma twilight_Fun_eqAxm (f : L'.(function_symbols))
: E.empty ⊢ twilight_frm (Fun_eqAxm f).