External Representation: topic graphs [Godel, Escher, Bach. Hofstadter 1979] Paradoxes - Lewis Carroll Turing - Halting problem Halting problem - Infinity Paradoxes - Infinity Infinity - Lewis Carroll Infinity - Unpredictably long searches Infinity - Recursion Infinity - Zeno Infinity - Paradoxes Lewis Carroll - Zeno Lewis Carroll - Wordplay Halting problem - Decision procedures BlooP and FlooP - AI Halting problem - Unpredictably long searches BlooP and FlooP - Unpredictably long searches BlooP and FlooP - Recursion Tarski - Truth vs. provability Tarski - Epimenides Tarski - Undecidability Paradoxes - Self-ref [...] 20