context: It is highly likely that Julius is a frog. Chances are slight that Jeff went to the bedroom. It is likely that John discarded the apple. It is unlikely that if either 'John discarded the apple' or 'Julius is a frog' but not both then Bernhard is a swan. It is probably not the case that if 'John discarded the apple' or 'Julius is a frog' or both then Brian is a lion. There is little chance that if 'Julius is a frog' or 'Jeff went to the bedroom' or both then Greg is a rhino.
hypothesis: We doubt that either 'Greg is a rhino' or 'Jeff went to the bedroom' but not both.
valid_hypothesis: We doubt that either 'Greg is a rhino' or 'Jeff went to the bedroom' but not both.
invalid_hypothesis: There is a very good chance that either 'Greg is a rhino' or 'Jeff went to the bedroom' 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
    0.9::factA.
    0.1::factB.
    0.7::factC.
    %hop1
    0.2::factX:-xor(factC,factA).
    0.25::factY:-or(factC,factA).
    0.1::factZ:-or(factA,factB).
  
    %hop2
    conclusion:-xor(factZ,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a rhino' or 'Jeff went to the bedroom' but not both.