Chances are about even that Mary went to the garden. It is probably the case that Greg is yellow. It is unlikely that Julius is gray. It is certain that if 'Mary went to the garden' or 'Greg is yellow' or both then John got the apple. It is unlikely that if 'Mary went to the garden' or 'Julius is gray' or both then Brian is a rhino. We believe that if 'Julius is gray' or 'Mary went to the garden' or both then Gertrude is a mouse.
It is unlikely that either 'Gertrude is a mouse' or 'Mary went to the garden' but not both.
It is unlikely that either 'Gertrude is a mouse' or 'Mary went to the garden' but not both.
It is highly likely that either 'Gertrude is a mouse' or 'Mary went to the garden' 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
  0.5::factA.
  0.7::factB.
  0.2::factC.
  %hop1
  1.0::factX:-or(factA,factB).
  0.2::factY:-or(factA,factC).
  0.75::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Gertrude is a mouse' or 'Mary went to the garden' but not both.