It is probable that John picked up the apple. We believe that Emily is a wolf. There is little chance that Greg is yellow. It is highly unlikely that if either 'John picked up the apple' or 'Emily is a wolf' but not both then Fred is in the office. There is little chance that if either 'Greg is yellow' or 'Emily is a wolf' but not both then Bernhard is white. Chances are slight that if 'John picked up the apple' or 'Emily is a wolf' or both then Julius is gray.
It is impossible that 'Julius is gray' or 'John picked up the apple' or both.
It is likely that 'Julius is gray' or 'John picked up the apple' or both.
It is impossible that 'Julius is gray' or 'John picked up the apple' 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
  0.7::factA.
  0.75::factB.
  0.1::factC.
  %hop1
  0.05::factX:-xor(factA,factB).
  0.1::factY:-xor(factC,factB).
  0.1::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Julius is gray' or 'John picked up the apple' or both.