It is improbable that Sandra left the football. It is highly unlikely that Brian is a swan. Chances are about even that Lily is a frog. There is a very good chance that if 'Lily is a frog' or 'Sandra left the football' or both then Jason is tired. It is impossible that if either 'Sandra left the football' or 'Brian is a swan' but not both then John put down the apple. Chances are about even that if 'Sandra left the football and Brian is a swan' then Mary went to the bedroom.
There is a very good chance that 'Brian is a swan' or 'John put down the apple' or both.
It is highly unlikely that 'Brian is a swan' or 'John put down the apple' or both.
There is a very good chance that 'Brian is a swan' or 'John put down 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
  0.1::factA.
  0.05::factB.
  0.5::factC.
  %hop1
  0.8::factX:-or(factC,factA).
  0.0::factY:-xor(factA,factB).
  0.5::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Brian is a swan' or 'John put down the apple' or both.