It is likely that Julius is white. It is highly unlikely that Greg is a lion. It is highly likely that Mary left the apple. We doubt that if 'Mary left the apple and Greg is a lion' then John moved to the office. We doubt that if 'Julius is white and Mary left the apple' then Brian is green. It is impossible that if either 'Greg is a lion' or 'Mary left the apple' but not both then Lily is a frog.
There is a better than even chance that either 'Brian is green' or 'Julius is white' but not both.
There is a better than even chance that either 'Brian is green' or 'Julius is white' but not both.
It is impossible that either 'Brian is green' or 'Julius is white' 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
  0.7::factA.
  0.05::factB.
  0.9::factC.
  %hop1
  0.2::factX:-and(factC,factB).
  0.2::factY:-and(factA,factC).
  0.0::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Brian is green' or 'Julius is white' but not both.