It is highly unlikely that Julius is gray. There is almost no chance that Greg is a frog. It is highly likely that Mary left the football. We believe that if either 'Julius is gray' or 'Greg is a frog' but not both then Sandra dropped the milk. There is a very good chance that if 'Julius is gray' or 'Greg is a frog' or both then Bernhard is a frog. It is highly unlikely that if 'Greg is a frog and Julius is gray' then Gertrude is a cat.
It is highly unlikely that 'Gertrude is a cat' or 'Bernhard is a frog' or both.
It is highly unlikely that 'Gertrude is a cat' or 'Bernhard is a frog' or both.
Chances are about even that 'Gertrude is a cat' or 'Bernhard is a frog' 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
  0.05::factA.
  0.02::factB.
  0.9::factC.
  %hop1
  0.75::factX:-xor(factA,factB).
  0.8::factY:-or(factA,factB).
  0.05::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Gertrude is a cat' or 'Bernhard is a frog' or both.