context: We doubt that Bernhard is gray. There is a very good chance that Greg is a swan. It is highly unlikely that Brian is yellow.
hypothesis: We believe that 'Brian is yellow and Greg is a swan'.
valid_hypothesis: It is highly unlikely that 'Brian is yellow and Greg is a swan'.
invalid_hypothesis: We believe that 'Brian is yellow and Greg is a swan'.
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
    0.2::factA.
    0.8::factB.
    0.05::factC.
    
  
    %hop2
    conclusion:-and(factC,factB).
  
    query(conclusion).
    
hypothesis_assertion: 'Brian is yellow and Greg is a swan'.