There is little chance that John went to the kitchen. It is probable that Brian is white. It is certain that Greg is a swan. It is probably not the case that if 'Brian is white' or 'John went to the kitchen' or both then Emily is a sheep. It is highly unlikely that if 'John went to the kitchen and Greg is a swan' then Bernhard is a frog. It is highly likely that if either 'John went to the kitchen' or 'Greg is a swan' but not both then Julius is a lion.
We doubt that 'Bernhard is a frog' or 'Greg is a swan' or both.
It is certain that 'Bernhard is a frog' or 'Greg is a swan' or both.
We doubt that 'Bernhard is a frog' or 'Greg is a swan' 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
  0.1::factA.
  0.7::factB.
  1.0::factC.
  %hop1
  0.25::factX:-or(factB,factA).
  0.05::factY:-and(factA,factC).
  0.9::factZ:-xor(factA,factC).

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

  query(conclusion).
  
'Bernhard is a frog' or 'Greg is a swan' or both.