There is little chance that Mary dropped the apple. It is certain that Jason is thirsty. We doubt that Sandra got the milk. It is highly likely that if 'Jason is thirsty and Sandra got the milk' then Lily is a swan. There is little chance that if 'Mary dropped the apple and Sandra got the milk' then Julius is a frog. It is almost certain that if 'Mary dropped the apple and Jason is thirsty' then Bernhard is green.
It is highly unlikely that 'Sandra got the milk' or 'Jason is thirsty' or both.
It is certain that 'Sandra got the milk' or 'Jason is thirsty' or both.
It is highly unlikely that 'Sandra got the milk' or 'Jason is thirsty' 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.
  1.0::factB.
  0.2::factC.
  %hop1
  0.9::factX:-and(factB,factC).
  0.1::factY:-and(factA,factC).
  0.95::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Sandra got the milk' or 'Jason is thirsty' or both.