We doubt that Bernhard is green. There is a very good chance that Fred is in the school. Chances are slight that Brian is a frog. Chances are about even that if 'Brian is a frog' or 'Fred is in the school' or both then Greg is a rhino. It is certain that if 'Brian is a frog and Fred is in the school' then Mary got the milk. It is impossible that if 'Bernhard is green and Brian is a frog' then Julius is a swan.
There is a very good chance that 'Fred is in the school' or 'Julius is a swan' or both.
There is a very good chance that 'Fred is in the school' or 'Julius is a swan' or both.
We doubt that 'Fred is in the school' or 'Julius is a swan' 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
  0.2::factA.
  0.8::factB.
  0.1::factC.
  %hop1
  0.5::factX:-or(factC,factB).
  1.0::factY:-and(factC,factB).
  0.0::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Fred is in the school' or 'Julius is a swan' or both.