Chances are about even that Winona is a mouse. We believe that Mary left the football. It is improbable that Greg is white. It is almost certain that if 'Winona is a mouse and Mary left the football' then Sandra dropped the milk. It is likely that if 'Winona is a mouse and Greg is white' then John went to the hallway. It is improbable that if 'Greg is white' or 'Winona is a mouse' or both then Bernhard is a frog.
It is certain that either 'John went to the hallway' or 'Sandra dropped the milk' but not both.
It is probably not the case that either 'John went to the hallway' or 'Sandra dropped the milk' but not both.
It is certain that either 'John went to the hallway' or 'Sandra dropped the milk' but not 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
  0.5::factA.
  0.75::factB.
  0.1::factC.
  %hop1
  0.95::factX:-and(factA,factB).
  0.7::factY:-and(factA,factC).
  0.1::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'John went to the hallway' or 'Sandra dropped the milk' but not both.