It is unlikely that Mary picked up the milk. It is likely that Sandra left the milk. It is probably the case that Julius is a frog. There is a better than even chance that if 'Julius is a frog and Sandra left the milk' then Greg is yellow. Chances are about even that if 'Sandra left the milk' or 'Julius is a frog' or both then Lily is a swan. It is certain that if 'Sandra left the milk and Mary picked up the milk' then Jessica is a cat.
Chances are about even that either 'Lily is a swan' or 'Julius is a frog' but not both.
Chances are about even that either 'Lily is a swan' or 'Julius is a frog' but not both.
It is highly unlikely that either 'Lily is a swan' or 'Julius is a frog' 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
  0.2::factA.
  0.7::factB.
  0.7::factC.
  %hop1
  0.6::factX:-and(factC,factB).
  0.5::factY:-or(factB,factC).
  1.0::factZ:-and(factB,factA).

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

  query(conclusion).
  
Either 'Lily is a swan' or 'Julius is a frog' but not both.