It is likely that Greg is white. Chances are about even that Lily is gray. It is probable that Bernhard is a frog. It is impossible that if either 'Lily is gray' or 'Greg is white' but not both then Gertrude is a mouse. It is unlikely that if 'Greg is white and Bernhard is a frog' then Julius is yellow. We doubt that if 'Greg is white and Lily is gray' then John dropped the apple.
It is probably not the case that 'Greg is white and Lily is gray'.
It is probably not the case that 'Greg is white and Lily is gray'.
It is certain that 'Greg is white and Lily is gray'.

  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
  0.7::factA.
  0.5::factB.
  0.7::factC.
  %hop1
  0.0::factX:-xor(factB,factA).
  0.2::factY:-and(factA,factC).
  0.2::factZ:-and(factA,factB).

  %hop2
  conclusion:-and(factA,factB).

  query(conclusion).
  
'Greg is white and Lily is gray'.