# What is the regular expression for strings containing at least one a and at least one b? [duplicate]

$L = \{w \in \{a, b, c\}^*\mid w\text{ contains at least one }a\text{ and at least one }b\}$.

what's the proper regular expression for the following language?

• Start with a regular expression for strings which contain, at some point, an $a$, and at a later point, a $b$. – Yuval Filmus Apr 15 '18 at 8:36