context: It is improbable that Winona is a sheep. We doubt that Sandra left the football. We believe that Brian is white. It is highly unlikely that if 'Brian is white' or 'Winona is a sheep' or both then Julius is a swan. There is almost no chance that if 'Winona is a sheep and Brian is white' then Bernhard is green. There is almost no chance that if either 'Winona is a sheep' or 'Brian is white' but not both then Mary went to the office.
hypothesis: We believe that either 'Bernhard is green' or 'Brian is white' but not both.
valid_hypothesis: We believe that either 'Bernhard is green' or 'Brian is white' but not both.
invalid_hypothesis: Chances are slight that either 'Bernhard is green' or 'Brian is white' but not both.
problog: 
    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.
    0.2::factB.
    0.75::factC.
    %hop1
    0.05::factX:-or(factC,factA).
    0.02::factY:-and(factA,factC).
    0.02::factZ:-xor(factA,factC).
  
    %hop2
    conclusion:-xor(factY,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Bernhard is green' or 'Brian is white' but not both.