play(player, game)

hi,

i do not understand why the last assert is possible, can anyone give me 
a hand? can i assert everything independent of the definitions made bevor?

thanks!

(DEFCONCEPT PLAYER)
(DEFCONCEPT GAME)
(DEFRELATION PLAY (?X ?Y)
   :=> (AND (PLAYER ?X) (GAME ?Y)))

// or (defrelation play ((?x player) (?y game)))

(ASSERT (CLOSED GAME))
(ASSERT (CLOSED PLAYER))
(ASSERT (PLAYER JANO))
(ASSERT (PLAYER CHESS))
(ASSERT (PLAY JANO CHESS))
(ASSERT (PLAY JANO JANO))


regards
k.janowicz