It is improbable that Greg is gray. It is likely that John put down the apple. It is certain that Bernhard is a frog. It is certain that if 'Greg is gray and John put down the apple' then Emily is a wolf. It is almost certain that if 'Bernhard is a frog and John put down the apple' then Brian is a swan. It is highly unlikely that if either 'Bernhard is a frog' or 'John put down the apple' but not both then Gertrude is a sheep.
It is highly unlikely that 'Brian is a swan and Greg is gray'.
It is highly unlikely that 'Brian is a swan and Greg is gray'.
It is likely that 'Brian is a swan and Greg 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
  0.1::factA.
  0.7::factB.
  1.0::factC.
  %hop1
  1.0::factX:-and(factA,factB).
  0.95::factY:-and(factC,factB).
  0.05::factZ:-xor(factC,factB).

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

  query(conclusion).
  
'Brian is a swan and Greg is gray'.