Credit: https://cs.stackexchange.com/a/60791

Here we give an involved proof to give strong evidence that there is no "pumping lemma for context-sensitive languages." The idea is that if there is one, then one can show that the "infinity" problem for that model is recognizable, but this is impossible for CSLs because that problem is unrecognizable (as we prove with linear bounded automata).

Timeline:
0:00 - Intro
1:20 - What does a "pumping lemma" mean?
6:45 - If the predicate exists, then Infinity Problem is recognizable
13:43 - Infinity Problem for LBAs is not recognizable

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