It is probable that Brian is green. It is highly unlikely that Winona is a mouse. We doubt that John left the apple. It is probable that if 'Brian is green and Winona is a mouse' then Julius is a lion. It is probably not the case that if 'Winona is a mouse and Brian is green' then Lily is a swan. It is improbable that if 'John left the apple' or 'Brian is green' or both then Greg is a lion.
We doubt that either 'Brian is green' or 'Julius is a lion' but not both.
It is probably the case that either 'Brian is green' or 'Julius is a lion' but not both.
We doubt that either 'Brian is green' or 'Julius is a lion' 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.
  0.2::factC.
  %hop1
  0.7::factX:-and(factA,factB).
  0.25::factY:-and(factB,factA).
  0.1::factZ:-or(factC,factA).

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

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