context: We believe that Julius is a rhino. There is little chance that Greg is a swan. We believe that John discarded the apple. It is probable that if either 'John discarded the apple' or 'Julius is a rhino' but not both then Bernhard is green. It is probably not the case that if either 'Julius is a rhino' or 'Greg is a swan' but not both then Mary went to the garden. It is almost certain that if either 'Julius is a rhino' or 'Greg is a swan' but not both then Sandra took the milk.
hypothesis: It is highly unlikely that either 'Greg is a swan' or 'John discarded the apple' but not both.
valid_hypothesis: It is likely that either 'Greg is a swan' or 'John discarded the apple' but not both.
invalid_hypothesis: It is highly unlikely that either 'Greg is a swan' or 'John discarded the apple' 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
    0.75::factA.
    0.1::factB.
    0.75::factC.
    %hop1
    0.7::factX:-xor(factC,factA).
    0.25::factY:-xor(factA,factB).
    0.95::factZ:-xor(factA,factB).
  
    %hop2
    conclusion:-xor(factB,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a swan' or 'John discarded the apple' but not both.