context: It is highly likely that John picked up the milk. We believe that Bernhard is a frog. We doubt that Greg is gray. Chances are slight that if 'Bernhard is a frog' or 'Greg is gray' or both then Sandra dropped the milk. There is a better than even chance that if 'Bernhard is a frog and Greg is gray' then Jeff left the apple. It is highly unlikely that if either 'Greg is gray' or 'Bernhard is a frog' but not both then Bill went to the office.
hypothesis: It is highly likely that 'Bill went to the office' or 'John picked up the milk' or both.
valid_hypothesis: It is highly likely that 'Bill went to the office' or 'John picked up the milk' or both.
invalid_hypothesis: Chances are slight that 'Bill went to the office' or 'John picked up the milk' or 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
    0.9::factA.
    0.75::factB.
    0.2::factC.
    %hop1
    0.1::factX:-or(factB,factC).
    0.6::factY:-and(factB,factC).
    0.05::factZ:-xor(factC,factB).
  
    %hop2
    conclusion:-or(factZ,factA).
  
    query(conclusion).
    
hypothesis_assertion: 'Bill went to the office' or 'John picked up the milk' or both.