From Wikipedia:

"What the Tortoise Said to Achilles" is a brief dialogue by Lewis Carroll which playfully problematises the foundations of logic. The dialogue alludes to one of Zeno's paradoxes of motion, in which Achilles could never overtake the tortoise in a race. In Lewis's dialogue, the tortoise challenges Achilles to use the force of logic to make him accept the conclusion of a simple deductive argument. Ultimately, Achilles fails, because the clever tortoise leads him into an infinite regression.