context: There is almost no chance that Julius is a swan. Chances are about even that Brian is a rhino. It is certain that Mary dropped the milk. It is certain that if 'Brian is a rhino' or 'Julius is a swan' or both then Greg is a frog. It is highly unlikely that if either 'Julius is a swan' or 'Mary dropped the milk' but not both then John discarded the apple. We doubt that if 'Julius is a swan and Brian is a rhino' then Emily is a mouse.
hypothesis: It is impossible that 'Brian is a rhino' or 'Greg is a frog' or both.
valid_hypothesis: Chances are about even that 'Brian is a rhino' or 'Greg is a frog' or both.
invalid_hypothesis: It is impossible that 'Brian is a rhino' or 'Greg is a frog' 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
    0.02::factA.
    0.5::factB.
    1.0::factC.
    %hop1
    1.0::factX:-or(factB,factA).
    0.05::factY:-xor(factA,factC).
    0.2::factZ:-and(factA,factB).
  
    %hop2
    conclusion:-or(factB,factX).
  
    query(conclusion).
    
hypothesis_assertion: 'Brian is a rhino' or 'Greg is a frog' or both.