context: It is probable that Gertrude is a sheep. It is unlikely that John moved to the garden. It is certain that Bernhard is a frog. We believe that if either 'Bernhard is a frog' or 'John moved to the garden' but not both then Fred dropped the apple. It is improbable that if 'Bernhard is a frog' or 'Gertrude is a sheep' or both then Winona is a mouse. It is likely that if 'Bernhard is a frog' or 'John moved to the garden' or both then Julius is a lion.
hypothesis: Chances are about even that either 'Gertrude is a sheep' or 'Fred dropped the apple' but not both.
valid_hypothesis: Chances are about even that either 'Gertrude is a sheep' or 'Fred dropped the apple' but not both.
invalid_hypothesis: There is almost no chance that either 'Gertrude is a sheep' or 'Fred dropped the apple' 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
    0.7::factA.
    0.2::factB.
    1.0::factC.
    %hop1
    0.75::factX:-xor(factC,factB).
    0.1::factY:-or(factC,factA).
    0.7::factZ:-or(factC,factB).
  
    %hop2
    conclusion:-xor(factA,factX).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Gertrude is a sheep' or 'Fred dropped the apple' but not both.