We believe that Greg is a swan. Chances are slight that Bernhard is a frog. It is highly unlikely that Sandra took the football. It is probably not the case that if 'Sandra took the football' or 'Greg is a swan' or both then Sumit is thirsty. There is a very good chance that if 'Greg is a swan and Sandra took the football' then John put down the apple. It is unlikely that if either 'Sandra took the football' or 'Greg is a swan' but not both then Mary is in the school.
Chances are slight that either 'Sumit is thirsty' or 'Greg is a swan' but not both.
There is a better than even chance that either 'Sumit is thirsty' or 'Greg is a swan' but not both.
Chances are slight that either 'Sumit is thirsty' or 'Greg is a swan' 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
  0.75::factA.
  0.1::factB.
  0.05::factC.
  %hop1
  0.25::factX:-or(factC,factA).
  0.8::factY:-and(factA,factC).
  0.2::factZ:-xor(factC,factA).

  %hop2
  conclusion:-xor(factX,factA).

  query(conclusion).
  
Either 'Sumit is thirsty' or 'Greg is a swan' but not both.