context: We doubt that Greg is a frog. It is likely that Emily is a wolf. There is a better than even chance that Bill went to the bedroom. It is highly unlikely that if 'Emily is a wolf' or 'Bill went to the bedroom' or both then John is in the garden. There is little chance that if 'Greg is a frog' or 'Emily is a wolf' or both then Sandra left the football. Chances are slight that if either 'Emily is a wolf' or 'Greg is a frog' but not both then Brian is green.
hypothesis: It is probable that either 'John is in the garden' or 'Greg is a frog' but not both.
valid_hypothesis: It is probably not the case that either 'John is in the garden' or 'Greg is a frog' but not both.
invalid_hypothesis: It is probable that either 'John is in the garden' or 'Greg 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
    0.2::factA.
    0.7::factB.
    0.6::factC.
    %hop1
    0.05::factX:-or(factB,factC).
    0.1::factY:-or(factA,factB).
    0.1::factZ:-xor(factB,factA).
  
    %hop2
    conclusion:-xor(factX,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'John is in the garden' or 'Greg is a frog' but not both.