context: It is probably the case that Lily is a frog. We believe that Bernhard is a rhino. There is little chance that Julius is a swan. It is probable that if 'Lily is a frog' or 'Julius is a swan' or both then Greg is yellow. It is certain that if either 'Julius is a swan' or 'Bernhard is a rhino' but not both then John took the football. There is almost no chance that if 'Julius is a swan' or 'Bernhard is a rhino' or both then Sandra dropped the apple.
hypothesis: It is likely that either 'Sandra dropped the apple' or 'Lily is a frog' but not both.
valid_hypothesis: It is likely that either 'Sandra dropped the apple' or 'Lily is a frog' but not both.
invalid_hypothesis: There is almost no chance that either 'Sandra dropped the apple' or 'Lily is a frog' 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.
    0.75::factB.
    0.1::factC.
    %hop1
    0.7::factX:-or(factA,factC).
    1.0::factY:-xor(factC,factB).
    0.02::factZ:-or(factC,factB).
  
    %hop2
    conclusion:-xor(factZ,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Sandra dropped the apple' or 'Lily is a frog' but not both.