context: It is certain that Greg is a swan. Chances are about even that Brian is yellow. Chances are about even that Lily is a frog. There is almost no chance that if 'Greg is a swan' or 'Lily is a frog' or both then Jason is tired. It is impossible that if either 'Greg is a swan' or 'Lily is a frog' but not both then John left the apple. There is a better than even chance that if either 'Brian is yellow' or 'Greg is a swan' but not both then Bernhard is green.
hypothesis: Chances are about even that either 'Brian is yellow' or 'John left the apple' but not both.
valid_hypothesis: Chances are about even that either 'Brian is yellow' or 'John left the apple' but not both.
invalid_hypothesis: It is highly unlikely that either 'Brian is yellow' or 'John left 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
    1.0::factA.
    0.5::factB.
    0.5::factC.
    %hop1
    0.02::factX:-or(factA,factC).
    0.0::factY:-xor(factA,factC).
    0.6::factZ:-xor(factB,factA).
  
    %hop2
    conclusion:-xor(factB,factY).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is yellow' or 'John left the apple' but not both.