It is likely that Greg is gray. Chances are about even that Gertrude is a mouse. There is almost no chance that Bernhard is a rhino. It is probably not the case that if 'Greg is gray and Gertrude is a mouse' then Brian is green. Chances are about even that if 'Bernhard is a rhino' or 'Greg is gray' or both then Lily is a swan. There is little chance that if 'Greg is gray and Gertrude is a mouse' then John moved to the office.
It is likely that either 'Bernhard is a rhino' or 'Greg is gray' but not both.
It is likely that either 'Bernhard is a rhino' or 'Greg is gray' but not both.
It is probably not the case that either 'Bernhard is a rhino' or 'Greg is gray' 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.
  0.5::factB.
  0.02::factC.
  %hop1
  0.25::factX:-and(factA,factB).
  0.5::factY:-or(factC,factA).
  0.1::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Bernhard is a rhino' or 'Greg is gray' but not both.