It is probable that Mary got the milk. There is almost no chance that Bernhard is a rhino. It is probably not the case that Gertrude is a cat. Chances are slight that if 'Bernhard is a rhino and Gertrude is a cat' then Greg is gray. There is a very good chance that if either 'Mary got the milk' or 'Gertrude is a cat' but not both then Emily is a sheep. It is probably not the case that if 'Bernhard is a rhino and Gertrude is a cat' then John went to the kitchen.
It is highly likely that 'Greg is gray' or 'Gertrude is a cat' or both.
It is probably not the case that 'Greg is gray' or 'Gertrude is a cat' or both.
It is highly likely that 'Greg is gray' or 'Gertrude is a cat' 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.
  0.02::factB.
  0.25::factC.
  %hop1
  0.1::factX:-and(factB,factC).
  0.8::factY:-xor(factA,factC).
  0.25::factZ:-and(factB,factC).

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

  query(conclusion).
  
'Greg is gray' or 'Gertrude is a cat' or both.