It is unlikely that Bernhard is a frog. Chances are slight that Brian is white. It is certain that Sandra left the milk. It is improbable that if 'Bernhard is a frog' or 'Sandra left the milk' or both then John moved to the garden. It is certain that if 'Sandra left the milk' or 'Brian is white' or both then Gertrude is a sheep. It is improbable that if 'Bernhard is a frog and Sandra left the milk' then Jessica is a mouse.
It is certain that 'Gertrude is a sheep' or 'Brian is white' or both.
It is certain that 'Gertrude is a sheep' or 'Brian is white' or both.
It is impossible that 'Gertrude is a sheep' or 'Brian is white' 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.
  0.1::factB.
  1.0::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  1.0::factY:-or(factC,factB).
  0.1::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Gertrude is a sheep' or 'Brian is white' or both.