context: We doubt that John took the milk. It is probable that Greg is gray. It is impossible that Mary went to the office.
hypothesis: We doubt that 'John took the milk' or 'Greg is gray' or both.
valid_hypothesis: We believe that 'John took the milk' or 'Greg is gray' or both.
invalid_hypothesis: We doubt that 'John took the milk' or 'Greg is gray' or 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
    0.2::factA.
    0.7::factB.
    0.0::factC.
    
  
    %hop2
    conclusion:-or(factA,factB).
  
    query(conclusion).
    
hypothesis_assertion: 'John took the milk' or 'Greg is gray' or both.