It is likely that John went to the bedroom. We believe that Bill left the football. Chances are slight that Emily is a cat. It is likely that if either 'Bill left the football' or 'John went to the bedroom' but not both then Greg is a swan. There is almost no chance that if 'Emily is a cat' or 'Bill left the football' or both then Lily is a frog. We doubt that if 'Emily is a cat and Bill left the football' then Mary discarded the milk.
It is probably the case that 'Greg is a swan' or 'Emily is a cat' or both.
It is probably not the case that 'Greg is a swan' or 'Emily is a cat' or both.
It is probably the case that 'Greg is a swan' or 'Emily is a cat' 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
  0.7::factA.
  0.75::factB.
  0.1::factC.
  %hop1
  0.7::factX:-xor(factB,factA).
  0.02::factY:-or(factC,factB).
  0.2::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Greg is a swan' or 'Emily is a cat' or both.