4 February 2000 [John David Stone]

• Created.

17 March 2000 [John David Stone]

• Last revised by Mr. Stone.
• This version available at http://www.cs.grinnell.edu/~stone/courses/scheme/spring-2000/preconditions-and-postconditions.xhtml

Friday, 15 September 2000 [Samuel A. Rebelsky]

• Removed narrative (now in a separate document).
• Added some problems.
• Reformatted significantly.

Monday, 18 September 2000 [Samuel A. Rebelsky]

• Fixed some formatting.
• Rearranged the first two problems.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2000F/Labs/prepost.html.

Thursday, 22 February 2001 [Samuel A. Rebelsky]

• Updated formatting.

Sunday, 4 March 2001 [Samuel A. Rebelsky]

• Updated the name of exercise 2.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2001S/Labs/prepost.html.

Thursday, 10 October 2002 [Samuel A. Rebelsky]

• Fixed typos.
• Reformatted slightly.
• Added some examples at the end.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2002F/Labs/prepost.html.

Tuesday, 4 February 2003 [Samuel A. Rebelsky]

• Slight updates to text.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS153/2003S/Labs/prepost.html.

Monday, 24 February 2003 [Samuel A. Rebelsky]

• Slight updates to text and formatting.
• Moved history into a separate document (and updated early history).

Monday, 29 September 2003 [Samuel A. Rebelsky]

• Added summary.
• Added a few notes.

Friday, 3 October 2003 [Samuel A. Rebelsky]

• Reworded a few problems.
• Added a question about index.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2003F/Labs/prepost.html.

Friday, 22 September 2006 [Samuel A. Rebelsky]

• Added link to PDF version.
• Updated the index-of problem (previously named index) to refer to the earlier assignment of a similar problem. (That assignment has not been given in previous semesters.)
• Other minor updates.
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2006F/Labs/prepost.html.

Sunday, 18 February 2007 [Samuel A. Rebelsky]

• Moved the final problme to the extra time section.
• Added a suggestion to add index-of to the library.
• Other, minor, updates.

Sunday, 7 October 2007 [Samuel A. Rebelsky]

• Almost completely rewritten to emphasize colors (and to deemphasize numeric recursion).
• This version available at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2007F/Labs/prepost-lab.html.