param nPeople := 11;

set PREFS := 
   1 3   1 5   1 8   2 5   2 9   3 4   3 5   4 1   4 5    4 10  
   5 6   5 1   6 1   6 9   7 3   7 8   8 9   8 7   9 10  10 11 ;