-- (c) MFES / CSI 

-- Games

sig G{
   a : one T,
   h : one T,
   d : one D,
   s : one G
}

-- Teams and dates

sig D,T {}

fact{

   (T->T) - iden = ~h.a        -- teams play all against each other
                               -- but don't play with themselves
   a.~a & h.~h in iden         -- no repeated games with exactly the same teams
   (a+h).~(a+h) & d.~d in iden -- no team playing twice on same day
   s = a.~h & h.~a             -- game isomorphism (yields the "symmetric game")
                               -- It is an isomorphism by construction: s = ~s
                               -- and it is a function :-)
}

run{} for exactly 4 T, 12 G, 6 D -- why 12? 12 = 4*(4-1)