There is almost no chance that Bernhard is white. We doubt that Fred dropped the apple. It is improbable that John took the football. It is probable that if 'John took the football and Fred dropped the apple' then Greg is white. There is a better than even chance that if 'Bernhard is white and Fred dropped the apple' then Gertrude is a sheep. It is unlikely that if either 'John took the football' or 'Bernhard is white' but not both then Lily is a lion.
There is a very good chance that either 'Fred dropped the apple' or 'John took the football' but not both.
It is probably not the case that either 'Fred dropped the apple' or 'John took the football' but not both.
There is a very good chance that either 'Fred dropped the apple' or 'John took the football' 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
  0.02::factA.
  0.2::factB.
  0.1::factC.
  %hop1
  0.7::factX:-and(factC,factB).
  0.6::factY:-and(factA,factB).
  0.2::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Fred dropped the apple' or 'John took the football' but not both.