Chances are slight that Bernhard is a swan. It is probably not the case that Winona is a mouse. It is almost certain that Mary dropped the milk. Chances are slight that if 'Bernhard is a swan' or 'Mary dropped the milk' or both then Brian is a lion. It is highly unlikely that if 'Mary dropped the milk and Winona is a mouse' then John went to the hallway. Chances are slight that if either 'Mary dropped the milk' or 'Bernhard is a swan' but not both then Greg is a swan.
There is little chance that 'Brian is a lion' or 'John went to the hallway' or both.
There is little chance that 'Brian is a lion' or 'John went to the hallway' or both.
It is likely that 'Brian is a lion' or 'John went to the hallway' 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.
  0.25::factB.
  0.95::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  0.05::factY:-and(factC,factB).
  0.1::factZ:-xor(factC,factA).

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

  query(conclusion).
  
'Brian is a lion' or 'John went to the hallway' or both.