It is impossible that John dropped the apple. There is a better than even chance that Daniel got the milk. There is almost no chance that Lily is a lion. It is probably the case that if 'John dropped the apple and Daniel got the milk' then Jeff discarded the milk. We doubt that if 'John dropped the apple and Daniel got the milk' then Mary went to the garden. There is a very good chance that if 'Daniel got the milk and Lily is a lion' then Greg is gray.
Chances are about even that either 'Greg is gray' or 'John dropped the apple' but not both.
It is impossible that either 'Greg is gray' or 'John dropped the apple' but not both.
Chances are about even that either 'Greg is gray' or 'John dropped the apple' 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
  0.0::factA.
  0.6::factB.
  0.02::factC.
  %hop1
  0.7::factX:-and(factA,factB).
  0.2::factY:-and(factA,factB).
  0.8::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Greg is gray' or 'John dropped the apple' but not both.