notation "\b H" non associative with precedence 90
for @{(proj2 … (eqb_true ???) $H)}.
+notation < "𝐃" non associative with precedence 90
+ for @{'bigD}.
+interpretation "DeqSet" 'bigD = (mk_DeqSet ???).
+
lemma eqb_false: ∀S:DeqSet.∀a,b:S.
(eqb ? a b) = false ↔ a ≠ b.
#S #a #b % #H