There is a better than even chance that Greg is a swan. It is unlikely that Gertrude is a sheep. There is almost no chance that Lily is a lion. It is highly likely that if either 'Gertrude is a sheep' or 'Greg is a swan' but not both then Jessica is a cat. There is little chance that if either 'Gertrude is a sheep' or 'Greg is a swan' but not both then Mary went to the kitchen. It is certain that if 'Lily is a lion and Greg is a swan' then John moved to the office.
It is highly unlikely that 'Mary went to the kitchen' or 'Greg is a swan' or both.
There is a better than even chance that 'Mary went to the kitchen' or 'Greg is a swan' or both.
It is highly unlikely that 'Mary went to the kitchen' or 'Greg is a swan' or 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
  0.6::factA.
  0.2::factB.
  0.02::factC.
  %hop1
  0.9::factX:-xor(factB,factA).
  0.1::factY:-xor(factB,factA).
  1.0::factZ:-and(factC,factA).

  %hop2
  conclusion:-or(factY,factA).

  query(conclusion).
  
'Mary went to the kitchen' or 'Greg is a swan' or both.