We doubt that Fred put down the apple. It is certain that John picked up the milk. It is certain that Lily is a frog. It is impossible that if 'Lily is a frog' or 'Fred put down the apple' or both then Emily is a mouse. It is likely that if 'Fred put down the apple and John picked up the milk' then Greg is a swan. It is probable that if 'Fred put down the apple and Lily is a frog' then Brian is yellow.
It is highly unlikely that 'Greg is a swan' or 'John picked up the milk' or both.
It is certain that 'Greg is a swan' or 'John picked up the milk' or both.
It is highly unlikely that 'Greg is a swan' or 'John picked up the milk' 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
  0.2::factA.
  1.0::factB.
  1.0::factC.
  %hop1
  0.0::factX:-or(factC,factA).
  0.7::factY:-and(factA,factB).
  0.7::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Greg is a swan' or 'John picked up the milk' or both.