context: It is highly likely that Greg is a lion. It is likely that Jeff put down the milk. There is little chance that Brian is a rhino. It is improbable that if 'Brian is a rhino and Jeff put down the milk' then Bernhard is a frog. We doubt that if 'Jeff put down the milk' or 'Greg is a lion' or both then Mary got the football. It is probably not the case that if 'Jeff put down the milk' or 'Brian is a rhino' or both then Julius is yellow.
hypothesis: It is probably not the case that either 'Mary got the football' or 'Brian is a rhino' but not both.
valid_hypothesis: It is probably not the case that either 'Mary got the football' or 'Brian is a rhino' but not both.
invalid_hypothesis: We believe that either 'Mary got the football' or 'Brian is a rhino' 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
    0.9::factA.
    0.7::factB.
    0.1::factC.
    %hop1
    0.1::factX:-and(factC,factB).
    0.2::factY:-or(factB,factA).
    0.25::factZ:-or(factB,factC).
  
    %hop2
    conclusion:-xor(factY,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary got the football' or 'Brian is a rhino' but not both.