It is probably not the case that Sandra took the football. It is impossible that Winona is a mouse. It is highly unlikely that John went to the garden. We doubt that if either 'John went to the garden' or 'Winona is a mouse' but not both then Daniel left the apple. It is certain that if 'Winona is a mouse and John went to the garden' then Brian is a lion. It is unlikely that if 'John went to the garden and Winona is a mouse' then Greg is a swan.
It is impossible that either 'Greg is a swan' or 'Winona is a mouse' but not both.
It is impossible that either 'Greg is a swan' or 'Winona is a mouse' but not both.
It is highly likely that either 'Greg is a swan' or 'Winona is a mouse' 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
  0.25::factA.
  0.0::factB.
  0.05::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  1.0::factY:-and(factB,factC).
  0.2::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Greg is a swan' or 'Winona is a mouse' but not both.