context: It is probable that Sandra dropped the apple. There is little chance that Gertrude is a cat. There is a very good chance that Greg is white. There is little chance that if either 'Gertrude is a cat' or 'Greg is white' but not both then Bill went to the kitchen. We believe that if 'Gertrude is a cat' or 'Sandra dropped the apple' or both then Brian is a rhino. We doubt that if 'Sandra dropped the apple and Greg is white' then Bernhard is a swan.
hypothesis: It is improbable that 'Bernhard is a swan' or 'Sandra dropped the apple' or both.
valid_hypothesis: It is probable that 'Bernhard is a swan' or 'Sandra dropped the apple' or both.
invalid_hypothesis: It is improbable that 'Bernhard is a swan' or 'Sandra dropped the apple' 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
    0.7::factA.
    0.1::factB.
    0.8::factC.
    %hop1
    0.1::factX:-xor(factB,factC).
    0.75::factY:-or(factB,factA).
    0.2::factZ:-and(factA,factC).
  
    %hop2
    conclusion:-or(factZ,factA).
  
    query(conclusion).
    
hypothesis_assertion: 'Bernhard is a swan' or 'Sandra dropped the apple' or both.