フィッグワン
$$ imp \ a \ b:=a\rightarrow b $$
$$ ref \ U \ R:= \forall x:U,R \ x \ x $$
$$ ref \ imp $$
Require Import Utf8. Set Implicit Arguments. Definition imp a b:=a → b. Definition ref U R:=∀x:U,R x x. Goal ref imp. Abort.