;Task:
Write a function that returns the longest common substring of two strings. 

Use it within a program that demonstrates sample output from the function, which will consist of the longest common substring between "thisisatest" and "testing123testing". 

Note that substrings are consecutive characters within a string.   This distinguishes them from subsequences, which is any sequence of characters within a string, even if there are extraneous characters in between them. 

Hence, the [[longest common subsequence]] between "thisisatest" and "testing123testing" is "tsitest", whereas the longest common sub''string'' is just "test".


{{Template:Strings}}


;References:
*[http://en.wikipedia.org/wiki/Generalized_suffix_tree Generalize Suffix Tree]
*[[Ukkonen’s Suffix Tree Construction]]
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