It is impossible that Sandra took the milk. It is highly likely that Greg is a frog. We believe that John moved to the office. We believe that if 'John moved to the office' or 'Greg is a frog' or both then Bernhard is gray. It is unlikely that if either 'Greg is a frog' or 'Sandra took the milk' but not both then Brian is green. There is little chance that if either 'Greg is a frog' or 'John moved to the office' but not both then Mary went to the bedroom.
There is a very good chance that 'Bernhard is gray' or 'Brian is green' or both.
There is a very good chance that 'Bernhard is gray' or 'Brian is green' or both.
It is probably not the case that 'Bernhard is gray' or 'Brian is green' 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.
  0.75::factC.
  %hop1
  0.75::factX:-or(factC,factB).
  0.2::factY:-xor(factB,factA).
  0.1::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Bernhard is gray' or 'Brian is green' or both.