context: Chances are about even that Brian is gray. We doubt that Julius is yellow. It is probable that John discarded the milk. There is a very good chance that if 'John discarded the milk' or 'Julius is yellow' or both then Greg is yellow. It is unlikely that if 'Julius is yellow' or 'John discarded the milk' or both then Sandra left the football. It is probable that if 'John discarded the milk' or 'Brian is gray' or both then Mary dropped the milk.
hypothesis: Chances are slight that 'Sandra left the football and Mary dropped the milk'.
valid_hypothesis: Chances are slight that 'Sandra left the football and Mary dropped the milk'.
invalid_hypothesis: We believe that 'Sandra left the football and Mary dropped 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
    0.5::factA.
    0.2::factB.
    0.7::factC.
    %hop1
    0.8::factX:-or(factC,factB).
    0.2::factY:-or(factB,factC).
    0.7::factZ:-or(factC,factA).
  
    %hop2
    conclusion:-and(factY,factZ).
  
    query(conclusion).
    
hypothesis_assertion: 'Sandra left the football and Mary dropped the milk'.