interpretation "constructive quaternary and" 'and4 x y z t = (And4 x y z t).
+record Iff (A,B:CProp) : CProp ≝
+ { if: A → B;
+ fi: B → A
+ }.
+
+interpretation "logical iff" 'iff x y = (Iff x y).
+
inductive exT (A:Type) (P:A→CProp) : CProp ≝
ex_introT: ∀w:A. P w → exT A P.