Previous Algorithm: Illustration
1) for each a Î T: Empty(a) := Æ because a Þ* e
2) for each r: A ® e Î P: Empty(A) := {e} because A Þ1 e [r]
Empty(A) = {e}
e
e
e
…
 e
• if A ® X1X2 … Xn Î P and Empty(Xi) = {e}
  for all i = 1,…,n then Empty(A) = {e}
•
A
X1
X2
…
Xn
3) Apply the following rules until no Empty set can be changed:
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