title: How can I tell that a language is context-free from first sight?
body: <p>My professor expects us to quickly tell if a given language is regular, context-free but not regular, or not context-free (in other words, without drawing a PDA, writing a context-free grammar, and using the pumping lemma for context-free languages).</p>
  
  <p>I'm aware of tips that help us quickly tell what a regular language is at first sight,but not whether or not a language is context free.</p>
  
  <p>Thank you.</p>