We believe that John got the apple. It is improbable that Mary went to the office. It is impossible that Bernhard is a swan. Chances are slight that if 'Mary went to the office' or 'John got the apple' or both then Lily is yellow. We believe that if 'Mary went to the office and John got the apple' then Greg is a lion. It is probably not the case that if either 'John got the apple' or 'Mary went to the office' but not both then Jeff left the football.
It is probably not the case that 'Jeff left the football' or 'Lily is yellow' or both.
It is probably not the case that 'Jeff left the football' or 'Lily is yellow' or both.
We believe that 'Jeff left the football' or 'Lily is yellow' 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
  0.75::factA.
  0.1::factB.
  0.0::factC.
  %hop1
  0.1::factX:-or(factB,factA).
  0.75::factY:-and(factB,factA).
  0.25::factZ:-xor(factA,factB).

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

  query(conclusion).
  
'Jeff left the football' or 'Lily is yellow' or both.