It is impossible that John dropped the apple. It is highly likely that Mary went to the bedroom. Chances are slight that Greg is a rhino. It is probably the case that if 'Greg is a rhino' or 'Mary went to the bedroom' or both then Lily is a lion. It is almost certain that if 'John dropped the apple and Mary went to the bedroom' then Gertrude is a mouse. It is probably not the case that if 'John dropped the apple and Mary went to the bedroom' then Bernhard is gray.
We believe that 'John dropped the apple' or 'Gertrude is a mouse' or both.
It is impossible that 'John dropped the apple' or 'Gertrude is a mouse' or both.
We believe that 'John dropped the apple' or 'Gertrude is a mouse' 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
  0.0::factA.
  0.9::factB.
  0.1::factC.
  %hop1
  0.7::factX:-or(factC,factB).
  0.95::factY:-and(factA,factB).
  0.25::factZ:-and(factA,factB).

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

  query(conclusion).
  
'John dropped the apple' or 'Gertrude is a mouse' or both.