context: It is probably the case that Brian is a swan. It is highly likely that Lily is a rhino. There is almost no chance that Winona is a sheep. It is certain that if 'Lily is a rhino and Brian is a swan' then Julius is a swan. There is almost no chance that if 'Brian is a swan and Lily is a rhino' then Jeff discarded the milk. There is a better than even chance that if 'Lily is a rhino' or 'Brian is a swan' or both then Fred went to the garden.
hypothesis: It is probably the case that either 'Brian is a swan' or 'Lily is a rhino' but not both.
valid_hypothesis: It is probably not the case that either 'Brian is a swan' or 'Lily is a rhino' but not both.
invalid_hypothesis: It is probably the case that either 'Brian is a swan' or 'Lily is a rhino' but not 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
    0.7::factA.
    0.9::factB.
    0.02::factC.
    %hop1
    1.0::factX:-and(factB,factA).
    0.02::factY:-and(factA,factB).
    0.6::factZ:-or(factB,factA).
  
    %hop2
    conclusion:-xor(factA,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is a swan' or 'Lily is a rhino' but not both.