It is likely that Lily is a swan. There is a very good chance that Bernhard is a frog. It is highly likely that Fred is in the cinema. It is highly unlikely that if either 'Lily is a swan' or 'Fred is in the cinema' but not both then Brian is white. We doubt that if 'Bernhard is a frog' or 'Fred is in the cinema' or both then Julius is a lion. It is improbable that if 'Lily is a swan' or 'Fred is in the cinema' or both then John moved to the garden.
It is almost certain that 'Lily is a swan' or 'Fred is in the cinema' or both.
It is almost certain that 'Lily is a swan' or 'Fred is in the cinema' or both.
Chances are about even that 'Lily is a swan' or 'Fred is in the cinema' 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.
  0.8::factB.
  0.9::factC.
  %hop1
  0.05::factX:-xor(factA,factC).
  0.2::factY:-or(factB,factC).
  0.1::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Lily is a swan' or 'Fred is in the cinema' or both.