context: Chances are slight that Jessica is a cat. It is probably the case that Greg is green. It is certain that John left the football. It is highly unlikely that if either 'Jessica is a cat' or 'Greg is green' but not both then Gertrude is a sheep. We believe that if 'John left the football and Jessica is a cat' then Brian is a rhino. It is probably the case that if either 'John left the football' or 'Greg is green' but not both then Julius is a swan.
hypothesis: It is certain that 'John left the football' or 'Julius is a swan' or both.
valid_hypothesis: It is certain that 'John left the football' or 'Julius is a swan' or both.
invalid_hypothesis: There is almost no chance that 'John left the football' or 'Julius is a swan' 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.
    0.7::factB.
    1.0::factC.
    %hop1
    0.05::factX:-xor(factA,factB).
    0.75::factY:-and(factC,factA).
    0.7::factZ:-xor(factC,factB).
  
    %hop2
    conclusion:-or(factC,factZ).
  
    query(conclusion).
    
hypothesis_assertion: 'John left the football' or 'Julius is a swan' or both.