There is little chance that John picked up the apple. Chances are about even that Yann is tired. Chances are about even that Julius is a frog. There is little chance that if 'John picked up the apple' or 'Julius is a frog' or both then Bernhard is white. There is little chance that if 'Julius is a frog' or 'John picked up the apple' or both then Greg is a lion. It is unlikely that if 'John picked up the apple and Yann is tired' then Mary left the milk.
There is a better than even chance that 'John picked up the apple' or 'Julius is a frog' or both.
There is a better than even chance that 'John picked up the apple' or 'Julius is a frog' or both.
It is impossible that 'John picked up the apple' or 'Julius 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.
  0.5::factB.
  0.5::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  0.1::factY:-or(factC,factA).
  0.2::factZ:-and(factA,factB).

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

  query(conclusion).
  
'John picked up the apple' or 'Julius is a frog' or both.