We believe that Greg is yellow. It is likely that John went to the office. It is probably the case that Brian is a rhino. Chances are about even that if either 'Greg is yellow' or 'Brian is a rhino' but not both then Sumit is thirsty. It is almost certain that if either 'John went to the office' or 'Brian is a rhino' but not both then Mary grabbed the milk. There is almost no chance that if 'Greg is yellow' or 'John went to the office' or both then Julius is a lion.
We believe that 'Greg is yellow' or 'Julius is a lion' or both.
We believe that 'Greg is yellow' or 'Julius is a lion' or both.
It is probably not the case that 'Greg is yellow' or 'Julius is a lion' 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
  0.75::factA.
  0.7::factB.
  0.7::factC.
  %hop1
  0.5::factX:-xor(factA,factC).
  0.95::factY:-xor(factB,factC).
  0.02::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Greg is yellow' or 'Julius is a lion' or both.