context: Chances are about even that Jessica is a cat. It is probably not the case that Greg is a frog. It is probably not the case that Julius is yellow. It is highly unlikely that if either 'Julius is yellow' or 'Greg is a frog' but not both then Sandra got the milk. Chances are slight that if 'Julius is yellow and Greg is a frog' then Lily is a rhino. There is little chance that if 'Julius is yellow and Greg is a frog' then Mary left the milk.
hypothesis: It is certain that 'Greg is a frog' or 'Mary left the milk' or both.
valid_hypothesis: It is probably not the case that 'Greg is a frog' or 'Mary left the milk' or both.
invalid_hypothesis: It is certain that 'Greg is a frog' or 'Mary left the milk' 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
    0.5::factA.
    0.25::factB.
    0.25::factC.
    %hop1
    0.05::factX:-xor(factC,factB).
    0.1::factY:-and(factC,factB).
    0.1::factZ:-and(factC,factB).
  
    %hop2
    conclusion:-or(factB,factZ).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is a frog' or 'Mary left the milk' or both.