It is probable that Mary dropped the milk. There is a very good chance that John picked up the apple. It is highly likely that Julius is a frog. It is probably the case that if either 'Julius is a frog' or 'John picked up the apple' but not both then Jessica is a cat. Chances are slight that if either 'John picked up the apple' or 'Mary dropped the milk' but not both then Sandra got the milk. There is little chance that if 'Julius is a frog and Mary dropped the milk' then Bernhard is a rhino.
It is highly unlikely that 'Julius is a frog' or 'Mary dropped the milk' or both.
It is almost certain that 'Julius is a frog' or 'Mary dropped the milk' or both.
It is highly unlikely that 'Julius is a frog' or 'Mary dropped 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
  0.7::factA.
  0.8::factB.
  0.9::factC.
  %hop1
  0.7::factX:-xor(factC,factB).
  0.1::factY:-xor(factB,factA).
  0.1::factZ:-and(factC,factA).

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

  query(conclusion).
  
'Julius is a frog' or 'Mary dropped the milk' or both.