It is probably the case that Sandra left the milk. We doubt that Brian is a swan. We believe that John took the football. It is probably the case that if 'John took the football and Brian is a swan' then Daniel dropped the apple. There is a very good chance that if 'John took the football and Sandra left the milk' then Lily is green. There is a very good chance that if either 'Brian is a swan' or 'Sandra left the milk' but not both then Greg is a rhino.
It is improbable that either 'Brian is a swan' or 'Sandra left the milk' but not both.
There is a better than even chance that either 'Brian is a swan' or 'Sandra left the milk' but not both.
It is improbable that either 'Brian is a swan' or 'Sandra left the milk' 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
  0.7::factA.
  0.2::factB.
  0.75::factC.
  %hop1
  0.7::factX:-and(factC,factB).
  0.8::factY:-and(factC,factA).
  0.8::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'Brian is a swan' or 'Sandra left the milk' but not both.