Chances are about even that Sandra left the football. Chances are about even that Mary dropped the apple. It is probable that Lily is white. It is impossible that if 'Mary dropped the apple' or 'Lily is white' or both then Brian is green. We doubt that if either 'Lily is white' or 'Sandra left the football' but not both then Greg is a rhino. We doubt that if 'Mary dropped the apple and Sandra left the football' then Julius is a swan.
It is improbable that 'Sandra left the football' or 'Mary dropped the apple' or both.
We believe that 'Sandra left the football' or 'Mary dropped the apple' or both.
It is improbable that 'Sandra left the football' or 'Mary dropped the apple' 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
  0.5::factA.
  0.5::factB.
  0.7::factC.
  %hop1
  0.0::factX:-or(factB,factC).
  0.2::factY:-xor(factC,factA).
  0.2::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Sandra left the football' or 'Mary dropped the apple' or both.