It is likely that Greg is yellow. It is highly unlikely that Yann is tired. Chances are slight that Sandra took the milk. We doubt that if either 'Sandra took the milk' or 'Yann is tired' but not both then John moved to the office. Chances are slight that if either 'Greg is yellow' or 'Yann is tired' but not both then Daniel got the football. It is certain that if 'Greg is yellow' or 'Yann is tired' or both then Julius is a frog.
It is probable that 'Daniel got the football' or 'Greg is yellow' or both.
It is probable that 'Daniel got the football' or 'Greg is yellow' or both.
There is little chance that 'Daniel got the football' or 'Greg 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
  0.7::factA.
  0.05::factB.
  0.1::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  0.1::factY:-xor(factA,factB).
  1.0::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Daniel got the football' or 'Greg is yellow' or both.