Add subdirectories

Add /ipynb/ and /py/ subdirectories to keep the home page neater.

README.md

@@ -2,46 +2,47 @@
 
 *Etudes* are exercises to practice or demonstrate skills, long used by piano players. 
 
-This project contains **pytudes**—Python programs to practice or demonstrate skills.
+This project contains **pytudes**—Python programs to practice or demonstrate skills. 
+Some are in Jupyter (IPython) notebooks, some in *.py files.
  
 # pytudes: Index of Jupyter (IPython) Notebooks
 
 |Logic and Number Puzzles|
 |---|
-|[Advent of Code 2016](https://github.com/norvig/pytudes/blob/master/Advent%20of%20Code.ipynb)<br>*Puzzle site with a coding puzzle each day for Advent 2016*|
-|[Translating English Sentences into Propositional Logic Statements](https://github.com/norvig/pytudes/blob/master/PropositionalLogic.ipynb)<br>*Automatically converting informal English sentences into formal Propositional Logic.*|
-|[The Puzzle of the Misanthropic Neighbors](https://github.com/norvig/pytudes/blob/master/Mean%20Misanthrope%20Density.ipynb)<br>*How crowded will this neighborhood be, if nobody wants to live next door to anyone else?*|
-|[Countdown to 2016](https://github.com/norvig/pytudes/blob/master/Countdown.ipynb)<br>*Solving the equation 10 _ 9 _ 8 _ 7 _ 6 _ 5 _ 4 _ 3 _ 2 _ 1 = 2016. From an Alex Bellos puzzle.*|
-|[Sicherman Dice](https://github.com/norvig/pytudes/blob/master/Sicherman%20Dice.ipynb)<br>*Find a pair of dice that is like a regular pair of dice, only different.*|
-|[Beal's Conjecture Revisited](https://github.com/norvig/pytudes/blob/master/Beal.ipynb)<br>*A search for counterexamples to Beal's Conjecture*|
-|[When is Cheryl's Birthday?](https://github.com/norvig/pytudes/blob/master/Cheryl.ipynb)<br>*Solving the "Cheryl's Birthday" logic puzzle.*|
-|[When Cheryl Met Eve: A Birthday Story](https://github.com/norvig/pytudes/blob/master/Cheryl-and-Eve.ipynb)<br>*Inventing new puzzles in the Style of Cheryl's Birthday.*|
-|[Sol Golomb's Rectangle Puzzle](https://github.com/norvig/pytudes/blob/master/Golomb-Puzzle.ipynb)<br>*A Puzzle involving placing rectangles of different sizes inside a square. Bonus: cryptarithmetic.*|
-|[WWW: Will Warriors Win?](https://github.com/norvig/pytudes/blob/master/WWW.ipynb)<br>*Golden State Warriors probability of winning the 2016 NBA title.*|
+|[Advent of Code 2016](https://github.com/norvig/pytudes/blob/master/ipynb/Advent%20of%20Code.ipynb)<br>*Puzzle site with a coding puzzle each day for Advent 2016*|
+|[Translating English Sentences into Propositional Logic Statements](https://github.com/norvig/pytudes/blob/master/ipynb/PropositionalLogic.ipynb)<br>*Automatically converting informal English sentences into formal Propositional Logic.*|
+|[The Puzzle of the Misanthropic Neighbors](https://github.com/norvig/pytudes/blob/master/ipynb/Mean%20Misanthrope%20Density.ipynb)<br>*How crowded will this neighborhood be, if nobody wants to live next door to anyone else?*|
+|[Countdown to 2016](https://github.com/norvig/pytudes/blob/master/ipynb/Countdown.ipynb)<br>*Solving the equation 10 _ 9 _ 8 _ 7 _ 6 _ 5 _ 4 _ 3 _ 2 _ 1 = 2016. From an Alex Bellos puzzle.*|
+|[Sicherman Dice](https://github.com/norvig/pytudes/blob/master/ipynb/Sicherman%20Dice.ipynb)<br>*Find a pair of dice that is like a regular pair of dice, only different.*|
+|[Beal's Conjecture Revisited](https://github.com/norvig/pytudes/blob/master/ipynb/Beal.ipynb)<br>*A search for counterexamples to Beal's Conjecture*|
+|[When is Cheryl's Birthday?](https://github.com/norvig/pytudes/blob/master/ipynb/Cheryl.ipynb)<br>*Solving the "Cheryl's Birthday" logic puzzle.*|
+|[When Cheryl Met Eve: A Birthday Story](https://github.com/norvig/pytudes/blob/master/ipynb/Cheryl-and-Eve.ipynb)<br>*Inventing new puzzles in the Style of Cheryl's Birthday.*|
+|[Sol Golomb's Rectangle Puzzle](https://github.com/norvig/pytudes/blob/master/ipynb/Golomb-Puzzle.ipynb)<br>*A Puzzle involving placing rectangles of different sizes inside a square. Bonus: cryptarithmetic.*|
+|[WWW: Will Warriors Win?](https://github.com/norvig/pytudes/blob/master/ipynb/WWW.ipynb)<br>*Golden State Warriors probability of winning the 2016 NBA title.*|
 
 |Word Games|
 |---|
-|[Ghost](https://github.com/norvig/pytudes/blob/master/Ghost.ipynb)<br>*The word game Ghost (add letters, try to avoid making a word).*|
-|[World's Longest Palindrome](https://github.com/norvig/pytudes/blob/master/pal3.ipynb)<br>*Searching for a long Panama-style palindrome, this time letter-by-letter.*|
-|[Refactoring a Crossword Game Program](https://github.com/norvig/pytudes/blob/master/Scrabble.ipynb)<br>*Refactoring the Scrabble / Word with Friends game from Udacity 212.*|
-|[xkcd 1313: Regex Golf](https://github.com/norvig/pytudes/blob/master/xkcd1313.ipynb)<br>*Find the smallest regular expression; inspired by Randall Monroe.*|
-|[xkcd 1313: Regex Golf (Part 2: Infinite Problems)](https://github.com/norvig/pytudes/blob/master/xkcd1313-part2.ipynb)<br>*Regex Golf: better, faster, funer. With Stefan Pochmann.*|
-|[Let's Code About Bike Locks](https://github.com/norvig/pytudes/blob/master/Fred%20Buns.ipynb)<br>*A tale of a bicycle combination lock that uses letters instead of digits. Inspired by Bike Snob NYC.*|
-|[Gesture Typing](https://github.com/norvig/pytudes/blob/master/Gesture%20Typing.ipynb)<br>*What word has the longest path on a gesture-typing smartphone keyboard? Inspired by Nicolas Schank and Shumin Zhai.*|
-|[How to Do Things with Words, or Statistical Natural Language Processing in Python](https://github.com/norvig/pytudes/blob/master/How%20to%20Do%20Things%20with%20Words.ipynb)<br>*Spelling Correction, Secret Codes, Word Segmentation, and more: grab your bag of words.*|
+|[Ghost](https://github.com/norvig/pytudes/blob/master/ipynb/Ghost.ipynb)<br>*The word game Ghost (add letters, try to avoid making a word).*|
+|[World's Longest Palindrome](https://github.com/norvig/pytudes/blob/master/ipynb/pal3.ipynb)<br>*Searching for a long Panama-style palindrome, this time letter-by-letter.*|
+|[Refactoring a Crossword Game Program](https://github.com/norvig/pytudes/blob/master/ipynb/Scrabble.ipynb)<br>*Refactoring the Scrabble / Word with Friends game from Udacity 212.*|
+|[xkcd 1313: Regex Golf](https://github.com/norvig/pytudes/blob/master/ipynb/xkcd1313.ipynb)<br>*Find the smallest regular expression; inspired by Randall Monroe.*|
+|[xkcd 1313: Regex Golf (Part 2: Infinite Problems)](https://github.com/norvig/pytudes/blob/master/ipynb/xkcd1313-part2.ipynb)<br>*Regex Golf: better, faster, funer. With Stefan Pochmann.*|
+|[Let's Code About Bike Locks](https://github.com/norvig/pytudes/blob/master/ipynb/Fred%20Buns.ipynb)<br>*A tale of a bicycle combination lock that uses letters instead of digits. Inspired by Bike Snob NYC.*|
+|[Gesture Typing](https://github.com/norvig/pytudes/blob/master/ipynb/Gesture%20Typing.ipynb)<br>*What word has the longest path on a gesture-typing smartphone keyboard? Inspired by Nicolas Schank and Shumin Zhai.*|
+|[How to Do Things with Words, or Statistical Natural Language Processing in Python](https://github.com/norvig/pytudes/blob/master/ipynb/How%20to%20Do%20Things%20with%20Words.ipynb)<br>*Spelling Correction, Secret Codes, Word Segmentation, and more: grab your bag of words.*|
 
 |Computer Science Algorithms, Concepts, and Problems|
 |---|
-|[A Chaos Game with Triangles](https://github.com/norvig/pytudes/blob/master/Sierpinski.ipynb)<br>*A surprising appearance of the Sierpinski triangle in a random walk between vertexes.*|
-|[BASIC Interpreter](https://github.com/norvig/pytudes/blob/master/BASIC.ipynb)<br>*How to write an interpreter for the BASIC programming language.*|
-|[Bad Grade, Good Experience](https://github.com/norvig/pytudes/blob/master/Snobol.ipynb)<br>*As a student, did you ever get a bad grade on a programming assignment? (Snobol, Concordance)*|
-|[Conway's Game of Life](https://github.com/norvig/pytudes/blob/master/Life.ipynb)<br>*The cellular automata zero-player game.*|
-|[A Concrete Introduction to Probability](https://github.com/norvig/pytudes/blob/master/Probability.ipynb)<br>*Code and examples of the basic principles of Probability Theory.*|
-|[Probability, Paradox, and the Reasonable Person Principle](https://github.com/norvig/pytudes/blob/master/ProbabilityParadox.ipynb)<br>*Some classic paradoxes in Probability Theory, and how too think about disagreements.*|
-|[The Convex Hull Problem](https://github.com/norvig/pytudes/blob/master/Convex%20Hull.ipynb)<br>*A classic Computer Science Algorithm.*|
-|[The Traveling Salesperson Problem](https://github.com/norvig/pytudes/blob/master/TSP.ipynb)<br>*Another of the classics.*|
-|[Economics Simulation](https://github.com/norvig/pytudes/blob/master/Economics.ipynb)<br>*A simulation of a simple economic game.*|
-|[Project Euler Utilities](https://github.com/norvig/pytudes/blob/master/Project%20Euler%20Utils.ipynb)<br>*My utility functions for the Project Euler problems, including `Primes` and `Factors`.*|
+|[A Chaos Game with Triangles](https://github.com/norvig/pytudes/blob/master/ipynb/Sierpinski.ipynb)<br>*A surprising appearance of the Sierpinski triangle in a random walk between vertexes.*|
+|[BASIC Interpreter](https://github.com/norvig/pytudes/blob/master/ipynb/BASIC.ipynb)<br>*How to write an interpreter for the BASIC programming language.*|
+|[Bad Grade, Good Experience](https://github.com/norvig/pytudes/blob/master/ipynb/Snobol.ipynb)<br>*As a student, did you ever get a bad grade on a programming assignment? (Snobol, Concordance)*|
+|[Conway's Game of Life](https://github.com/norvig/pytudes/blob/master/ipynb/Life.ipynb)<br>*The cellular automata zero-player game.*|
+|[A Concrete Introduction to Probability](https://github.com/norvig/pytudes/blob/master/ipynb/Probability.ipynb)<br>*Code and examples of the basic principles of Probability Theory.*|
+|[Probability, Paradox, and the Reasonable Person Principle](https://github.com/norvig/pytudes/blob/master/ipynb/ProbabilityParadox.ipynb)<br>*Some classic paradoxes in Probability Theory, and how too think about disagreements.*|
+|[The Convex Hull Problem](https://github.com/norvig/pytudes/blob/master/ipynb/Convex%20Hull.ipynb)<br>*A classic Computer Science Algorithm.*|
+|[The Traveling Salesperson Problem](https://github.com/norvig/pytudes/blob/master/ipynb/TSP.ipynb)<br>*Another of the classics.*|
+|[Economics Simulation](https://github.com/norvig/pytudes/blob/master/ipynb/Economics.ipynb)<br>*A simulation of a simple economic game.*|
+|[Project Euler Utilities](https://github.com/norvig/pytudes/blob/master/ipynb/Project%20Euler%20Utils.ipynb)<br>*My utility functions for the Project Euler problems, including `Primes` and `Factors`.*|
 
 # pytudes: Index of Python Files
 
@@ -50,25 +51,26 @@ The following are not notebooks, but raw `.py` files, although some of them have
 
 | **File** | **Description** | **Documentation**|
 |:--------|:-------------------|----|
-|[SET.py](https://github.com/norvig/pytudes/blob/master/SET.py)|Analyze the card game [SET](http://www.setgame.com/set).|[SET.html](http://norvig.com/SET.html)|
-|[beal.py](https://github.com/norvig/pytudes/blob/master/beal.py)|Search for counterexamples to Beal's Conjecture|[beal.html](http://norvig.com/beal.html)
-|[docex.py](https://github.com/norvig/pytudes/blob/master/docex.py)|A framework for running unit tests, similar to `doctest`.|
-|[ibol.py](https://github.com/norvig/pytudes/blob/master/ibol.py)|An Exercise in Species Barcoding|[ibol.html](http://norvig.com/ibol.html)
-|[lettercount.py](https://github.com/norvig/pytudes/blob/master/lettercount.py)|Convert Google Ngram Counts to Letter Counts|[mayzner.html](http://norvig.com/mayzner.html)
-|[lis.py](https://github.com/norvig/pytudes/blob/master/lis.py)|Lisp Interpreter written in Python|[lispy.html](http://norvig.com/lispy.html)
-|[lispy.py](https://github.com/norvig/pytudes/blob/master/lispy.py)|Even Better Lisp Interpreter written in Python|[lispy2.html](http://norvig.com/lispy2.html)
-|[lispytest.py](https://github.com/norvig/pytudes/blob/master/lispytest.py)|Tests for Lisp Interpreters|
-|[pal.py](https://github.com/norvig/pytudes/blob/master/pal.py)|Find long palindromes|[palindrome.html](http://norvig.com/palindrome.html)
-|[pal2.py](https://github.com/norvig/pytudes/blob/master/pal2.py)|Find longer palindromes|[palindrome.html](http://norvig.com/palindrome.html)
-|[pal3.py](https://github.com/norvig/pytudes/blob/master/pal3.py)|Find even longer palindromes|[palindrome.html](http://norvig.com/palindrome.html)
-|[py2html.py](https://github.com/norvig/pytudes/blob/master/py2html.py)|Pretty-printer to format Python files as html|
-|[spell.py](https://github.com/norvig/pytudes/blob/master/spell.py)|Spelling corrector|[spell-correct.html](http://norvig.com/spell-correct.html)
-|[sudoku.py](https://github.com/norvig/pytudes/blob/master/sudoku.py)|Program to solve sudoku puzzles|[sudoku.html](http://norvig.com/sudoku.html)
-|[testaccum.py](https://github.com/norvig/pytudes/blob/master/testaccum.py)|Tests for my failed Python `accumulation display` proposal|[pyacc.html](http://norvig.com/pyacc.html)
-|[yaptu.py](https://github.com/norvig/pytudes/blob/master/yaptu.py)|Yet Another Python Templating Utility|
+|[SET.py](https://github.com/norvig/pytudes/blob/master/py/SET.py)|Analyze the card game [SET](http://www.setgame.com/set).|[SET.html](http://norvig.com/SET.html)|
+|[beal.py](https://github.com/norvig/pytudes/blob/master/py/beal.py)|Search for counterexamples to Beal's Conjecture|[beal.html](http://norvig.com/beal.html)
+|[docex.py](https://github.com/norvig/pytudes/blob/master/py/docex.py)|A framework for running unit tests, similar to `doctest`.|
+|[ibol.py](https://github.com/norvig/pytudes/blob/master/py/ibol.py)|An Exercise in Species Barcoding|[ibol.html](http://norvig.com/ibol.html)
+|[lettercount.py](https://github.com/norvig/pytudes/blob/master/py/lettercount.py)|Convert Google Ngram Counts to Letter Counts|[mayzner.html](http://norvig.com/mayzner.html)
+|[lis.py](https://github.com/norvig/pytudes/blob/master/py/lis.py)|Lisp Interpreter written in Python|[lispy.html](http://norvig.com/lispy.html)
+|[lispy.py](https://github.com/norvig/pytudes/blob/master/py/lispy.py)|Even Better Lisp Interpreter written in Python|[lispy2.html](http://norvig.com/lispy2.html)
+|[lispytest.py](https://github.com/norvig/pytudes/blob/master/py/lispytest.py)|Tests for Lisp Interpreters|
+|[pal.py](https://github.com/norvig/pytudes/blob/master/py/pal.py)|Find long palindromes|[palindrome.html](http://norvig.com/palindrome.html)
+|[pal2.py](https://github.com/norvig/pytudes/blob/master/py/pal2.py)|Find longer palindromes|[palindrome.html](http://norvig.com/palindrome.html)
+|[pal3.py](https://github.com/norvig/pytudes/blob/master/py/pal3.py)|Find even longer palindromes|[palindrome.html](http://norvig.com/palindrome.html)
+|[py2html.py](https://github.com/norvig/pytudes/blob/master/py/py2html.py)|Pretty-printer to format Python files as html|
+|[spell.py](https://github.com/norvig/pytudes/blob/master/py/spell.py)|Spelling corrector|[spell-correct.html](http://norvig.com/spell-correct.html)
+|[sudoku.py](https://github.com/norvig/pytudes/blob/master/py/sudoku.py)|Program to solve sudoku puzzles|[sudoku.html](http://norvig.com/sudoku.html)
+|[testaccum.py](https://github.com/norvig/pytudes/blob/master/py/testaccum.py)|Tests for my failed Python `accumulation display` proposal|[pyacc.html](http://norvig.com/pyacc.html)
+|[yaptu.py](https://github.com/norvig/pytudes/blob/master/py/yaptu.py)|Yet Another Python Templating Utility|
 
 # Etudes for Programmers
 
-I got the idea for the "etudes" part of the name from this [1978 book by Charles Wetherell](https://books.google.com/books/about/Etudes_for_programmers.html?id=u89WAAAAMAAJ):
+I got the idea for the "etudes" part of the name from this [1978 book by Charles Wetherell](https://books.google.com/books/about/Etudes_for_programmers.html?id=u89WAAAAMAAJ)
+that was very influential to me when I was learning to program around 1980.
 
 ![](https://images-na.ssl-images-amazon.com/images/I/51ZnZH29dvL._SX394_BO1,204,203,200_.jpg)