There is almost no chance that John dropped the apple. It is likely that Bernhard is a frog. We believe that Greg is a swan. There is a better than even chance that if 'Greg is a swan' or 'Bernhard is a frog' or both then Jeff left the apple. There is little chance that if either 'Greg is a swan' or 'Bernhard is a frog' but not both then Mary went to the hallway. Chances are about even that if 'Bernhard is a frog' or 'John dropped the apple' or both then Brian is a lion.
Chances are about even that 'Mary went to the hallway' or 'Brian is a lion' or both.
Chances are about even that 'Mary went to the hallway' or 'Brian is a lion' or both.
It is impossible that 'Mary went to the hallway' or 'Brian is a lion' 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
  0.02::factA.
  0.7::factB.
  0.75::factC.
  %hop1
  0.6::factX:-or(factC,factB).
  0.1::factY:-xor(factC,factB).
  0.5::factZ:-or(factB,factA).

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

  query(conclusion).
  
'Mary went to the hallway' or 'Brian is a lion' or both.