context: It is probably the case that Fred dropped the milk. There is little chance that Mary got the football. It is improbable that Greg is a swan. Chances are about even that if 'Greg is a swan and Fred dropped the milk' then Bernhard is yellow. It is unlikely that if either 'Mary got the football' or 'Greg is a swan' but not both then Lily is white. There is a better than even chance that if 'Fred dropped the milk and Greg is a swan' then Brian is green.
hypothesis: It is highly unlikely that either 'Greg is a swan' or 'Brian is green' but not both.
valid_hypothesis: It is highly unlikely that either 'Greg is a swan' or 'Brian is green' but not both.
invalid_hypothesis: It is almost certain that either 'Greg is a swan' or 'Brian is green' 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.
    0.1::factB.
    0.1::factC.
    %hop1
    0.5::factX:-and(factC,factA).
    0.2::factY:-xor(factB,factC).
    0.6::factZ:-and(factA,factC).
  
    %hop2
    conclusion:-xor(factC,factZ).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a swan' or 'Brian is green' but not both.