Let S be a set of words. We want to decide if there exists a word w so that sub_{w}(n)=S for some n. The applet below allows us to do this. It works as follows. Enter a word from S into the input box and then click "Add". Do this with each word in S one by one. The applet will then tell you if there exists a word w so that S=sub_{w}(n) for some n. Click "Clear" if you want to start again. 

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