+inductive ex (A:Type) (P:A→Prop) : Type \def
+ ex_intro: ∀w:A. P w → ex A P.
+
+notation < "hvbox(Σ ident i opt (: ty) break . p)"
+ right associative with precedence 20
+for @{ 'sigma ${default
+ @{\lambda ${ident i} : $ty. $p)}
+ @{\lambda ${ident i} . $p}}}.
+
+interpretation "constructive exists" 'sigma \eta.x =
+ (cic:/matita/constructive_connectives/ex.ind#xpointer(1/1) _ x).