It is probable that Julius is a swan. There is little chance that Gertrude is a mouse. It is probably not the case that John picked up the milk. There is a very good chance that if 'Julius is a swan' or 'Gertrude is a mouse' or both then Mary went to the office. We doubt that if 'John picked up the milk and Gertrude is a mouse' then Emily is a wolf. It is impossible that if 'Gertrude is a mouse' or 'John picked up the milk' or both then Greg is a lion.
It is likely that 'Mary went to the office' or 'John picked up the milk' or both.
It is likely that 'Mary went to the office' or 'John picked up the milk' or both.
It is impossible that 'Mary went to the office' or 'John picked up the milk' 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.
  0.1::factB.
  0.25::factC.
  %hop1
  0.8::factX:-or(factA,factB).
  0.2::factY:-and(factC,factB).
  0.0::factZ:-or(factB,factC).

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

  query(conclusion).
  
'Mary went to the office' or 'John picked up the milk' or both.