We want to thank Alexander Sczyrba for his help, especially in creating the figures, and the over 100 students, authors, instructors and consultants around the world. In spite of the great distances we sometimes wonder whether their office isn't just a few footsteps away...
Randy Glasbergen
gave his permission to use one of his cartoons
in section C. Thank you :-)
The Earth image was contributed by N. Blom.