There is almost no chance that Brian is a rhino. There is almost no chance that Antoine is thirsty. There is little chance that Greg is a swan. There is a better than even chance that if 'Brian is a rhino and Greg is a swan' then Bernhard is a frog. It is certain that if either 'Brian is a rhino' or 'Antoine is thirsty' but not both then John picked up the milk. There is almost no chance that if 'Brian is a rhino and Greg is a swan' then Mary left the football.
There is little chance that either 'Greg is a swan' or 'Brian is a rhino' but not both.
There is little chance that either 'Greg is a swan' or 'Brian is a rhino' but not both.
It is almost certain that either 'Greg is a swan' or 'Brian is a rhino' 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
  0.02::factA.
  0.02::factB.
  0.1::factC.
  %hop1
  0.6::factX:-and(factA,factC).
  1.0::factY:-xor(factA,factB).
  0.02::factZ:-and(factA,factC).

  %hop2
  conclusion:-xor(factC,factA).

  query(conclusion).
  
Either 'Greg is a swan' or 'Brian is a rhino' but not both.