Chances are slight that Bernhard is a rhino. Chances are slight that Julius is a frog. There is little chance that John took the football. Chances are slight that if 'Bernhard is a rhino and Julius is a frog' then Lily is a swan. It is impossible that if 'John took the football and Bernhard is a rhino' then Emily is a sheep. It is likely that if 'Julius is a frog and Bernhard is a rhino' then Mary discarded the milk.
It is impossible that either 'Mary discarded the milk' or 'Emily is a sheep' but not both.
It is impossible that either 'Mary discarded the milk' or 'Emily is a sheep' but not both.
There is a very good chance that either 'Mary discarded the milk' or 'Emily is a sheep' 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.
  0.1::factC.
  %hop1
  0.1::factX:-and(factA,factB).
  0.0::factY:-and(factC,factA).
  0.7::factZ:-and(factB,factA).

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

  query(conclusion).
  
Either 'Mary discarded the milk' or 'Emily is a sheep' but not both.