It is certain that Julius is a frog. There is little chance that John left the milk. It is probably not the case that Greg is a swan. Chances are about even that if 'Greg is a swan' or 'John left the milk' or both then Lily is gray. There is a very good chance that if 'Julius is a frog and John left the milk' then Mary went to the office. It is likely that if 'Greg is a swan and John left the milk' then Jessica is a sheep.
It is unlikely that 'Lily is gray' or 'Julius is a frog' or both.
It is certain that 'Lily is gray' or 'Julius is a frog' or both.
It is unlikely that 'Lily is gray' or 'Julius is a frog' or 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
  1.0::factA.
  0.1::factB.
  0.25::factC.
  %hop1
  0.5::factX:-or(factC,factB).
  0.8::factY:-and(factA,factB).
  0.7::factZ:-and(factC,factB).

  %hop2
  conclusion:-or(factX,factA).

  query(conclusion).
  
'Lily is gray' or 'Julius is a frog' or both.