context: It is impossible that Bernhard is a rhino. There is little chance that Greg is a frog. It is probable that John took the apple. Chances are about even that if 'Greg is a frog and Bernhard is a rhino' then Daniel left the milk. Chances are about even that if 'Greg is a frog and John took the apple' then Lily is yellow. It is highly likely that if 'John took the apple' or 'Bernhard is a rhino' or both then Sandra dropped the milk.
hypothesis: We doubt that either 'Lily is yellow' or 'John took the apple' but not both.
valid_hypothesis: It is likely that either 'Lily is yellow' or 'John took the apple' but not both.
invalid_hypothesis: We doubt that either 'Lily is yellow' or 'John took 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
    0.0::factA.
    0.1::factB.
    0.7::factC.
    %hop1
    0.5::factX:-and(factB,factA).
    0.5::factY:-and(factB,factC).
    0.9::factZ:-or(factC,factA).
  
    %hop2
    conclusion:-xor(factY,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Lily is yellow' or 'John took the apple' but not both.