I've come across this problem in my studies, and I've abstracted it to the more general case here.Given a finite alphabet, what is a regular expression that matches all strings over the alphabet, except one particular finite substring?As an example:Given $\Sigma = \{a, b, c\}$What is a regular expression that matches all of $\Sigma$ except the substring $ba$?What I really want is simply $\Sigma^* - ba$. 
What is a regular expression that matches all strings over the alphabet except a particular substring?
formal languages;regular languages;regular expressions