Lemma 6.4.2: each regular expression is equivalent to one in a sum of products form.
Lemma 6.4.3: for languages W, X ___* that are infinite
telescoping unions, W = _ Yk and X = _ Zk,
where Yk _ Yk+1 and Zk _ Zk+1 for all k0, union and concatenation can be performed component-wise
W _ X = _ (Yk _ Zk), and WX = _ (YkZk).
k=0
k=0
k=0
k=0
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