It is likely that Mary dropped the milk. There is a better than even chance that John went to the office. It is highly likely that Greg is a rhino. It is almost certain that if 'Greg is a rhino and Mary dropped the milk' then Lily is a swan. It is likely that if either 'John went to the office' or 'Mary dropped the milk' but not both then Brian is yellow. It is highly likely that if 'Greg is a rhino and John went to the office' then Gertrude is a cat.
Chances are slight that either 'Greg is a rhino' or 'Brian is yellow' but not both.
There is a better than even chance that either 'Greg is a rhino' or 'Brian is yellow' but not both.
Chances are slight that either 'Greg is a rhino' or 'Brian is yellow' 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.
  0.6::factB.
  0.9::factC.
  %hop1
  0.95::factX:-and(factC,factA).
  0.7::factY:-xor(factB,factA).
  0.9::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Greg is a rhino' or 'Brian is yellow' but not both.