context: It is highly likely that Brian is a rhino. Chances are about even that Bernhard is a swan. Chances are slight that John picked up the milk. It is highly likely that if 'Brian is a rhino and John picked up the milk' then Yann is bored. It is highly unlikely that if either 'John picked up the milk' or 'Bernhard is a swan' but not both then Jessica is a mouse. It is likely that if 'Brian is a rhino and Bernhard is a swan' then Greg is gray.
hypothesis: There is almost no chance that 'Greg is gray and John picked up the milk'.
valid_hypothesis: There is almost no chance that 'Greg is gray and John picked up the milk'.
invalid_hypothesis: It is highly likely that 'Greg is gray and John picked up the milk'.
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.
    0.5::factB.
    0.1::factC.
    %hop1
    0.9::factX:-and(factA,factC).
    0.05::factY:-xor(factC,factB).
    0.7::factZ:-and(factA,factB).
  
    %hop2
    conclusion:-and(factZ,factC).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is gray and John picked up the milk'.