See also Gary Levin's Manual for ISETL, which is in isetldoc.zip, which is downloadable from the Math Archives (ISETL for DOS, Macintosh, Unix).
isetldoc.zip contains three text files, isetl.1, isetl.2, isetl.3, which are parts 1 - 3 of the Manual to ISETL version 3. The underlying ISETL engine in ISETLW (all versions) is essentially unchanged from ISETL (for DOS, Macintosh, Unix) version 3, August, 1990.