Your Name
CS 4301
Lab 5
{x | x in {a, b}* and that have a substring of length four that
     begins and ends with the same symbol}

Input:  aab --- invalid input ---

Input:  aba --- invalid input ---

Input:  baa --- invalid input ---

Input:  babab --- invalid input ---

Input:  aabbb --- invalid input ---

Input:  bbbaa --- invalid input ---

Input:  abbba --- invalid input ---

Input:  aabbbbb *** valid input ***

Input:  bbbbbbbaa *** valid input ***

Input:  bbbabbbabbb *** valid input ***

Input:   --- invalid input ---

Input:  a --- invalid input ---

Input:  b --- invalid input ---

Input:  aa --- invalid input ---

Input:  ab --- invalid input ---

Input:  ba --- invalid input ---

Input:  bb --- invalid input ---

Input:  aaa --- invalid input ---

Input:  baa --- invalid input ---

Input:  aba --- invalid input ---

Input:  bbb --- invalid input ---

Input:  abba *** valid input ***

Input:  baba --- invalid input ---

Input:  babba *** valid input ***

Input:  abbbba *** valid input ***

Input:  bbabababa *** valid input ***

Input:  bbaaaabaaa *** valid input ***

Input:  babaaabaaa *** valid input ***

Input:  abaaaaaaaaaaa *** valid input ***

Input:  bababaabababa *** valid input ***