(send (self) 0)
(send (self) 1)
(send (self) 2)
(send (self) 3)
(send (self) 4)
(send (self) 5)
(check (and (= (recv ((? x) x)) 0)
(= (recv ((? x) x)) 1)
(= (recv ((? x) x)) 2)
(= (recv ((? x) x)) 3)
(= (recv ((? x) x)) 4)
(= (recv ((? x) x)) 5)))