It is likely that Daniel got the football. It is improbable that Bernhard is yellow. Chances are about even that Lily is a frog. Chances are about even that if either 'Lily is a frog' or 'Bernhard is yellow' but not both then Mary went to the office. It is certain that if 'Daniel got the football' or 'Lily is a frog' or both then John left the football. We believe that if 'Daniel got the football and Bernhard is yellow' then Greg is white.
We believe that 'Daniel got the football' or 'Mary went to the office' or both.
We believe that 'Daniel got the football' or 'Mary went to the office' or both.
It is improbable that 'Daniel got the football' or 'Mary went to the office' 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
  0.7::factA.
  0.1::factB.
  0.5::factC.
  %hop1
  0.5::factX:-xor(factC,factB).
  1.0::factY:-or(factA,factC).
  0.75::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Daniel got the football' or 'Mary went to the office' or both.