@@ -1,10 +1,13 @@
 # TODO
 
-- get object rotation: 3 Euler angles. Attempt made at `gravity.cpp`
-- get object velocity and angular velocity
-- what is the point of motion state?
-- Stairs physics: http://gamedev.stackexchange.com/questions/74794/make-the-player-run-onto-stairs-smoothly
-- Voronoi: https://www.youtube.com/watch?v=FIPu9_OGFgc
-- substeps vs smaller time step on stepSimulation?
-- opengl visualization
-- user input
+-   get object rotation: 3 Euler angles. Attempt made at `gravity.cpp`
+-   get object velocity and angular velocity
+-   what is the point of motion state?
+-   Stairs physics: http://gamedev.stackexchange.com/questions/74794/make-the-player-run-onto-stairs-smoothly
+-   Voronoi: https://www.youtube.com/watch?v=FIPu9_OGFgc
+-   substeps vs smaller time step on stepSimulation?
+-   opengl visualization
+-   user input
+-   2D
+    - http://gamedev.stackexchange.com/questions/22319/how-to-disable-y-axis-movement-in-the-bullet-physics-engine
+    - http://gamedev.stackexchange.com/questions/6130/is-it-worth-it-to-use-bullet-for-2d-physics-instead-of-box2d-for-the-sake-of-lea
@@ -1,10 +1,17 @@
 # glibc
 
 1.  [Introduction](introduction.md)
-1.  Usage
+1.  Examples
+    1.  [alloca.c](alloca.c)
+    1.  [brk.c](brk.c)
     1.  [main.c](main.c)
+    1.  [ptrace.c](ptrace.c)
+    1.  [reboot.c](reboot.c.off)
     1.  [syscall.c](syscall.c)
-    1.  [alloca.c](alloca.c)
+    1.  `string.h`
+        1.  [strverscmp.c](strverscmp.c)
+    1.  TODO
+        1.  [sendfile.c](sendfile.c.off)
 1.  Internals
     1.  [Makefile](makefile.md)
     1.  [Source tree](source-tree.md)
 
@@ -0,0 +1,30 @@
+/*
+http://stackoverflow.com/questions/15057010/comparing-version-numbers-in-c/37015135#37015135
+*/
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(void) {
+    assert(strverscmp("1.2.3" , "1.2.3" ) == 0);
+    assert(strverscmp("1.2.3" , "1.2.4" )  < 0);
+    assert(strverscmp("1.2.3" , "1.2.2" )  > 0);
+    assert(strverscmp("9.2.3" , "10.2.3")  < 0);
+    assert(strverscmp("10.2.3", "9.2.3" )  > 0);
+
+    /* Delimiers are also compared. */
+    assert(strverscmp("1a2", "1b2" ) < 0);
+    assert(strverscmp("1b2", "1a2" ) > 0);
+
+    /* Leading 0s: number gets treated as 0.X, e.g. 01 means 0.1.
+     * Maybe not perfect for version strings, but sane version strings
+     * should not have trailing 0s.
+     */
+    assert(strverscmp("01", "9" ) < 0);
+    assert(strverscmp("01", "09") < 0);
+    assert(strverscmp("01", "09") < 0);
+    assert(strverscmp("09", "1")  < 0);
+    return EXIT_SUCCESS;
+}