It is impossible that Mary left the milk. It is probable that Brian is gray. It is likely that Greg is a frog. Chances are slight that if either 'Brian is gray' or 'Greg is a frog' but not both then Julius is white. Chances are about even that if 'Brian is gray' or 'Mary left the milk' or both then John put down the apple. It is probably the case that if 'Brian is gray' or 'Mary left the milk' or both then Lily is yellow.
It is highly unlikely that 'Lily is yellow' or 'Julius is white' or both.
Chances are about even that 'Lily is yellow' or 'Julius is white' or both.
It is highly unlikely that 'Lily is yellow' or 'Julius is white' 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
  0.0::factA.
  0.7::factB.
  0.7::factC.
  %hop1
  0.1::factX:-xor(factB,factC).
  0.5::factY:-or(factB,factA).
  0.7::factZ:-or(factB,factA).

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

  query(conclusion).
  
'Lily is yellow' or 'Julius is white' or both.