It is probably the case that Bernhard is a rhino. It is highly unlikely that Julius is gray. It is probably the case that Gertrude is a cat. It is impossible that if either 'Gertrude is a cat' or 'Julius is gray' but not both then John grabbed the apple. It is highly likely that if 'Julius is gray' or 'Gertrude is a cat' or both then Greg is green. It is probably not the case that if 'Julius is gray and Gertrude is a cat' then Mary went to the hallway.
It is improbable that 'Greg is green' or 'Julius is gray' or both.
There is a better than even chance that 'Greg is green' or 'Julius is gray' or both.
It is improbable that 'Greg is green' or 'Julius is gray' 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
  0.7::factA.
  0.05::factB.
  0.7::factC.
  %hop1
  0.0::factX:-xor(factC,factB).
  0.9::factY:-or(factB,factC).
  0.25::factZ:-and(factB,factC).

  %hop2
  conclusion:-or(factY,factB).

  query(conclusion).
  
'Greg is green' or 'Julius is gray' or both.