Let S be a set.

The Kleene closure of S, denoted S∗, is the set of all finite sequences in S.

Examples:

Example of Kleene star applied to set of strings:

{"ab","c"}* = {ε, "ab", "c", "abab", "abc", "cab", "cc", "ababab", "ababc", "abcab", "abcc", "cabab", "cabc", "ccab", "ccc", ...}.

Example …