context: It is unlikely that Mary went to the hallway. It is probably the case that Greg is a swan. It is impossible that Sandra left the football.
hypothesis: It is unlikely that either 'Mary went to the hallway' or 'Sandra left the football' but not both.
valid_hypothesis: It is unlikely that either 'Mary went to the hallway' or 'Sandra left the football' but not both.
invalid_hypothesis: It is almost certain that either 'Mary went to the hallway' or 'Sandra left the football' 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
    0.2::factA.
    0.7::factB.
    0.0::factC.
    
  
    %hop2
    conclusion:-xor(factA,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary went to the hallway' or 'Sandra left the football' but not both.