There is a better than even chance that Lily is a frog. It is improbable that John got the apple. There is almost no chance that Brian is white. It is impossible that if either 'Lily is a frog' or 'Brian is white' but not both then Emily is a wolf. It is highly unlikely that if 'Brian is white and Lily is a frog' then Sandra dropped the milk. We believe that if 'Lily is a frog and John got the apple' then Mary went to the hallway.
We believe that either 'Sandra dropped the milk' or 'Mary went to the hallway' but not both.
It is highly unlikely that either 'Sandra dropped the milk' or 'Mary went to the hallway' but not both.
We believe that either 'Sandra dropped the milk' or 'Mary went to the hallway' 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
  0.6::factA.
  0.1::factB.
  0.02::factC.
  %hop1
  0.0::factX:-xor(factA,factC).
  0.05::factY:-and(factC,factA).
  0.75::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Sandra dropped the milk' or 'Mary went to the hallway' but not both.