There is almost no chance that Julius is white. It is probably the case that Bernhard is a frog. It is probable that Mary took the milk. There is little chance that if 'Julius is white' or 'Mary took the milk' or both then Greg is a frog. It is certain that if either 'Mary took the milk' or 'Bernhard is a frog' but not both then John got the apple. It is impossible that if 'Bernhard is a frog and Julius is white' then Lily is a swan.
It is impossible that 'Greg is a frog and Lily is a swan'.
It is impossible that 'Greg is a frog and Lily is a swan'.
It is probable that 'Greg is a frog and Lily is a swan'.

  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
  0.02::factA.
  0.7::factB.
  0.7::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  1.0::factY:-xor(factC,factB).
  0.0::factZ:-and(factB,factA).

  %hop2
  conclusion:-and(factX,factZ).

  query(conclusion).
  
'Greg is a frog and Lily is a swan'.