1. 13Computability
   1. 13.1Turing Machines
      1. 13.1.1Diagram of a Turing Machine
      2. 13.1.2Turing Machine Cycle
   2. 13.2A Scheme Model of Turing Machines
      1. 13.2.1Exercise
      2. 13.2.2read-symbol
      3. 13.2.3lookup-state-symbol
      4. 13.2.4write-new-symbol
      5. 13.2.5new-position
      6. 13.2.6turing
   3. 13.3Turing Machines and Other Computer Designs
   4. 13.4Class P Problems and Intractable Problems
   5. 13.5Problems With No Solutions
      1. 13.5.1The Halting Problem
      2. 13.5.2The Halting Problem is not Computable
      3. 13.5.3Halting Problem Proof
   6. 13.6Bibliography