Chances are slight that Jessica is a wolf. It is probable that Lily is a frog. We believe that Bernhard is green. It is unlikely that if either 'Bernhard is green' or 'Lily is a frog' but not both then Jeff left the football. There is little chance that if 'Lily is a frog' or 'Jessica is a wolf' or both then John took the apple. There is a better than even chance that if 'Lily is a frog and Jessica is a wolf' then Brian is a swan.
It is improbable that 'Jeff left the football' or 'Brian is a swan' or both.
It is improbable that 'Jeff left the football' or 'Brian is a swan' or both.
There is a better than even chance that 'Jeff left the football' or 'Brian is a swan' 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.
  0.7::factB.
  0.75::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  0.1::factY:-or(factB,factA).
  0.6::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Jeff left the football' or 'Brian is a swan' or both.