It is highly unlikely that John went to the bedroom. It is impossible that Sandra left the milk. It is probably not the case that Gertrude is a wolf. There is a very good chance that if 'Gertrude is a wolf' or 'John went to the bedroom' or both then Jason is thirsty. It is impossible that if 'Gertrude is a wolf' or 'John went to the bedroom' or both then Jessica is a cat. There is little chance that if 'Sandra left the milk and Gertrude is a wolf' then Greg is a swan.
It is almost certain that 'Greg is a swan' or 'Jason is thirsty' or both.
It is probably not the case that 'Greg is a swan' or 'Jason is thirsty' or both.
It is almost certain that 'Greg is a swan' or 'Jason is thirsty' 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
  0.05::factA.
  0.0::factB.
  0.25::factC.
  %hop1
  0.8::factX:-or(factC,factA).
  0.0::factY:-or(factC,factA).
  0.1::factZ:-and(factB,factC).

  %hop2
  conclusion:-or(factZ,factX).

  query(conclusion).
  
'Greg is a swan' or 'Jason is thirsty' or both.