There is a very good chance that Gertrude is a mouse. It is probable that Bernhard is a swan. It is improbable that Brian is green. Chances are about even that if either 'Bernhard is a swan' or 'Brian is green' but not both then Sumit is thirsty. It is highly unlikely that if 'Gertrude is a mouse and Brian is green' then John got the football. Chances are slight that if 'Bernhard is a swan' or 'Brian is green' or both then Jeff went to the garden.
There is almost no chance that either 'Bernhard is a swan' or 'Brian is green' but not both.
It is likely that either 'Bernhard is a swan' or 'Brian is green' but not both.
There is almost no chance that either 'Bernhard is a swan' or 'Brian is green' but not both.

  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
  0.8::factA.
  0.7::factB.
  0.1::factC.
  %hop1
  0.5::factX:-xor(factB,factC).
  0.05::factY:-and(factA,factC).
  0.1::factZ:-or(factB,factC).

  %hop2
  conclusion:-xor(factB,factC).

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Brian is green' but not both.