It is impossible that John went to the hallway. We believe that Gertrude is a sheep. It is highly unlikely that Mary left the football. It is improbable that if 'Mary left the football and John went to the hallway' then Greg is a swan. It is unlikely that if 'Mary left the football' or 'Gertrude is a sheep' or both then Julius is a rhino. Chances are slight that if either 'Gertrude is a sheep' or 'John went to the hallway' but not both then Bernhard is gray.
It is improbable that 'Mary left the football' or 'Gertrude is a sheep' or both.
We believe that 'Mary left the football' or 'Gertrude is a sheep' or both.
It is improbable that 'Mary left the football' or 'Gertrude is a sheep' 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
  0.0::factA.
  0.75::factB.
  0.05::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.2::factY:-or(factC,factB).
  0.1::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Mary left the football' or 'Gertrude is a sheep' or both.