Chances are slight that John took the apple. It is highly unlikely that Emily is a sheep. It is unlikely that Mary dropped the milk. There is almost no chance that if 'Mary dropped the milk' or 'John took the apple' or both then Bill left the football. It is certain that if either 'Mary dropped the milk' or 'John took the apple' but not both then Lily is a frog. It is almost certain that if 'Emily is a sheep' or 'Mary dropped the milk' or both then Bernhard is a swan.
We believe that 'Mary dropped the milk' or 'Lily is a frog' or both.
It is probably not the case that 'Mary dropped the milk' or 'Lily is a frog' or both.
We believe that 'Mary dropped the milk' or 'Lily is a frog' 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.
  0.2::factC.
  %hop1
  0.02::factX:-or(factC,factA).
  1.0::factY:-xor(factC,factA).
  0.95::factZ:-or(factB,factC).

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

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