context: It is almost certain that Jeff left the apple. Chances are slight that Bernhard is a rhino. It is impossible that Brian is a swan. It is highly likely that if 'Brian is a swan' or 'Bernhard is a rhino' or both then Greg is a swan. Chances are about even that if either 'Brian is a swan' or 'Jeff left the apple' but not both then Bill went to the office. Chances are slight that if 'Jeff left the apple' or 'Brian is a swan' or both then Lily is a frog.
hypothesis: It is improbable that 'Greg is a swan' or 'Brian is a swan' or both.
valid_hypothesis: It is improbable that 'Greg is a swan' or 'Brian is a swan' or both.
invalid_hypothesis: There is a better than even chance that 'Greg is a swan' or 'Brian is a swan' 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
    0.95::factA.
    0.1::factB.
    0.0::factC.
    %hop1
    0.9::factX:-or(factC,factB).
    0.5::factY:-xor(factC,factA).
    0.1::factZ:-or(factA,factC).
  
    %hop2
    conclusion:-or(factX,factC).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is a swan' or 'Brian is a swan' or both.