GNU Autoconf, Automake and Libtool,
by G. V. Vaughan, B. Elliston, T. Tromey, and I. L. Taylor. SAMS (originally
New Riders), 2000, ISBN 1578701902.
 Because M4 is not aware of Sh code,
especially conditionals, some optimizations that look nice statically
may produce incorrect results at runtime.
Yet another great name from Lars J. Aas.