There is little chance that Greg is a swan. It is improbable that Mary dropped the milk. It is almost certain that Jessica is a mouse. It is likely that if either 'Jessica is a mouse' or 'Greg is a swan' but not both then Emily is a sheep. We doubt that if either 'Jessica is a mouse' or 'Greg is a swan' but not both then Sandra took the football. It is highly unlikely that if 'Jessica is a mouse' or 'Greg is a swan' or both then Julius is a rhino.
We doubt that either 'Mary dropped the milk' or 'Greg is a swan' but not both.
We doubt that either 'Mary dropped the milk' or 'Greg is a swan' but not both.
It is probably the case that either 'Mary dropped the milk' 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
  0.1::factA.
  0.1::factB.
  0.95::factC.
  %hop1
  0.7::factX:-xor(factC,factA).
  0.2::factY:-xor(factC,factA).
  0.05::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Mary dropped the milk' or 'Greg is a swan' but not both.