context: It is impossible that Mary got the apple. Chances are slight that Bernhard is a swan. We doubt that Greg is a rhino. We doubt that if either 'Greg is a rhino' or 'Mary got the apple' but not both then Yann is tired. It is probably not the case that if 'Mary got the apple' or 'Greg is a rhino' or both then John moved to the garden. We believe that if 'Greg is a rhino' or 'Bernhard is a swan' or both then Julius is a frog.
hypothesis: We doubt that 'Greg is a rhino' or 'Yann is tired' or both.
valid_hypothesis: We doubt that 'Greg is a rhino' or 'Yann is tired' or both.
invalid_hypothesis: There is a very good chance that 'Greg is a rhino' or 'Yann is tired' 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
    0.0::factA.
    0.1::factB.
    0.2::factC.
    %hop1
    0.2::factX:-xor(factC,factA).
    0.25::factY:-or(factA,factC).
    0.75::factZ:-or(factC,factB).
  
    %hop2
    conclusion:-or(factC,factX).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is a rhino' or 'Yann is tired' or both.