There is little chance that Bernhard is a rhino. It is certain that John dropped the milk. There is little chance that Brian is yellow. It is likely that if 'John dropped the milk' or 'Bernhard is a rhino' or both then Lily is a frog. There is almost no chance that if either 'Brian is yellow' or 'John dropped the milk' but not both then Greg is a swan. There is little chance that if 'John dropped the milk and Brian is yellow' then Mary went to the office.
It is likely that either 'Lily is a frog' or 'Brian is yellow' but not both.
It is likely that either 'Lily is a frog' or 'Brian is yellow' but not both.
It is improbable that either 'Lily is a frog' or 'Brian is yellow' 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
  0.1::factA.
  1.0::factB.
  0.1::factC.
  %hop1
  0.7::factX:-or(factB,factA).
  0.02::factY:-xor(factC,factB).
  0.1::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Lily is a frog' or 'Brian is yellow' but not both.