context: We believe that John took the football. It is impossible that Bill went to the kitchen. It is highly likely that Greg is a swan. It is highly unlikely that if 'Bill went to the kitchen and John took the football' then Brian is white. It is improbable that if 'John took the football' or 'Greg is a swan' or both then Bernhard is a frog. Chances are slight that if 'John took the football and Bill went to the kitchen' then Lily is gray.
hypothesis: There is little chance that either 'Greg is a swan' or 'Bill went to the kitchen' but not both.
valid_hypothesis: It is highly likely that either 'Greg is a swan' or 'Bill went to the kitchen' but not both.
invalid_hypothesis: There is little chance that either 'Greg is a swan' or 'Bill went to the kitchen' 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.
    0.0::factB.
    0.9::factC.
    %hop1
    0.05::factX:-and(factB,factA).
    0.1::factY:-or(factA,factC).
    0.1::factZ:-and(factA,factB).
  
    %hop2
    conclusion:-xor(factC,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a swan' or 'Bill went to the kitchen' but not both.