It is likely that Bernhard is gray. It is highly unlikely that Mary discarded the apple. It is almost certain that Greg is a frog. It is highly unlikely that if either 'Mary discarded the apple' or 'Bernhard is gray' but not both then Fred is in the office. It is unlikely that if either 'Greg is a frog' or 'Bernhard is gray' but not both then Julius is white. It is almost certain that if 'Greg is a frog' or 'Mary discarded the apple' or both then John dropped the milk.
We doubt that 'Greg is a frog and Bernhard is gray'.
It is likely that 'Greg is a frog and Bernhard is gray'.
We doubt that 'Greg is a frog and Bernhard 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.
  0.05::factB.
  0.95::factC.
  %hop1
  0.05::factX:-xor(factB,factA).
  0.2::factY:-xor(factC,factA).
  0.95::factZ:-or(factC,factB).

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

  query(conclusion).
  
'Greg is a frog and Bernhard is gray'.