It is likely that Greg is a rhino. It is unlikely that Emily is a sheep. We doubt that John went to the hallway. It is impossible that if 'Greg is a rhino and John went to the hallway' then Mary got the milk. It is highly unlikely that if 'Emily is a sheep and Greg is a rhino' then Lily is a swan. It is likely that if 'Emily is a sheep and Greg is a rhino' then Brian is a frog.
It is probable that either 'Mary got the milk' or 'Greg is a rhino' but not both.
It is probable that either 'Mary got the milk' or 'Greg is a rhino' but not both.
Chances are slight that either 'Mary got the milk' or 'Greg is a rhino' 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.
  0.2::factC.
  %hop1
  0.0::factX:-and(factA,factC).
  0.05::factY:-and(factB,factA).
  0.7::factZ:-and(factB,factA).

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

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