context: There is little chance that John dropped the apple. It is unlikely that Brian is a frog. It is certain that Bernhard is a swan. It is almost certain that if 'Bernhard is a swan' or 'John dropped the apple' or both then Julius is green. It is impossible that if 'Bernhard is a swan' or 'John dropped the apple' or both then Daniel grabbed the milk. It is unlikely that if either 'Brian is a frog' or 'John dropped the apple' but not both then Mary went to the office.
hypothesis: It is probably the case that either 'Mary went to the office' or 'Brian is a frog' but not both.
valid_hypothesis: We doubt that either 'Mary went to the office' or 'Brian is a frog' but not both.
invalid_hypothesis: It is probably the case that either 'Mary went to the office' or 'Brian 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
    0.1::factA.
    0.2::factB.
    1.0::factC.
    %hop1
    0.95::factX:-or(factC,factA).
    0.0::factY:-or(factC,factA).
    0.2::factZ:-xor(factB,factA).
  
    %hop2
    conclusion:-xor(factZ,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary went to the office' or 'Brian is a frog' but not both.