There is almost no chance that Brian is a lion. Chances are slight that Fred left the apple. We doubt that John went to the bedroom. There is a better than even chance that if 'John went to the bedroom and Fred left the apple' then Daniel took the football. We doubt that if 'Fred left the apple' or 'Brian is a lion' or both then Greg is green. There is a very good chance that if 'Brian is a lion and Fred left the apple' then Mary dropped the milk.
It is highly likely that either 'Greg is green' or 'Brian is a lion' but not both.
It is highly unlikely that either 'Greg is green' or 'Brian is a lion' but not both.
It is highly likely that either 'Greg is green' or 'Brian 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
  0.02::factA.
  0.1::factB.
  0.2::factC.
  %hop1
  0.6::factX:-and(factC,factB).
  0.2::factY:-or(factB,factA).
  0.8::factZ:-and(factA,factB).

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

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