We doubt that Bernhard is a lion. It is certain that Gertrude is a cat. It is almost certain that John moved to the office. We doubt that if 'John moved to the office' or 'Gertrude is a cat' or both then Brian is white. It is probably not the case that if either 'Bernhard is a lion' or 'Gertrude is a cat' but not both then Sandra took the apple. There is a better than even chance that if 'Bernhard is a lion and Gertrude is a cat' then Greg is yellow.
We believe that 'Greg is yellow' or 'Bernhard is a lion' or both.
We doubt that 'Greg is yellow' or 'Bernhard is a lion' or both.
We believe that 'Greg is yellow' or 'Bernhard 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
  0.2::factA.
  1.0::factB.
  0.95::factC.
  %hop1
  0.2::factX:-or(factC,factB).
  0.25::factY:-xor(factA,factB).
  0.6::factZ:-and(factA,factB).

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

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