It is probably the case that Greg is a swan. Chances are about even that Brian is a lion. Chances are slight that Lily is a rhino. There is little chance that if 'Brian is a lion and Lily is a rhino' then Mary went to the hallway. It is almost certain that if 'Lily is a rhino and Brian is a lion' then Antoine is thirsty. It is almost certain that if 'Brian is a lion' or 'Lily is a rhino' or both then Emily is a wolf.
It is highly unlikely that either 'Brian is a lion' or 'Emily is a wolf' but not both.
It is highly unlikely that either 'Brian is a lion' or 'Emily is a wolf' but not both.
It is highly likely that either 'Brian is a lion' or 'Emily is a wolf' but not both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.7::factA.
  0.5::factB.
  0.1::factC.
  %hop1
  0.1::factX:-and(factB,factC).
  0.95::factY:-and(factC,factB).
  0.95::factZ:-or(factB,factC).

  %hop2
  conclusion:-xor(factB,factZ).

  query(conclusion).
  
Either 'Brian is a lion' or 'Emily is a wolf' but not both.