context: There is little chance that Greg is a swan. It is probably not the case that Brian is white. It is highly likely that Bernhard is a swan. There is almost no chance that if either 'Brian is white' or 'Bernhard is a swan' but not both then Jason is thirsty. It is certain that if 'Bernhard is a swan' or 'Greg is a swan' or both then John went to the bedroom. There is a very good chance that if either 'Bernhard is a swan' or 'Greg is a swan' but not both then Mary got the football.
hypothesis: We believe that 'Greg is a swan' or 'Mary got the football' or both.
valid_hypothesis: We believe that 'Greg is a swan' or 'Mary got the football' or both.
invalid_hypothesis: It is improbable that 'Greg is a swan' or 'Mary got the football' or 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
    0.1::factA.
    0.25::factB.
    0.9::factC.
    %hop1
    0.02::factX:-xor(factB,factC).
    1.0::factY:-or(factC,factA).
    0.8::factZ:-xor(factC,factA).
  
    %hop2
    conclusion:-or(factA,factZ).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is a swan' or 'Mary got the football' or both.