Here . means single character and * means any number of preceding element
so ".*" should match any strings duplicated by single letter like "aa", "aaaa"," bbbbbb", "bbbbbbbb".
For case "ab", if '.' means 'a', then 'b' will not be matched, and if '.' means 'b' then 'a' is not matched, how can we get a true for this case?
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