The not command returns true if a is false.  Otherwise false is returned.

This is slightly different than in Maple T.A. proper, which understands 1.0 and 0.0 as true and false.  Because Maple does not equate numbers as boolean conditionals, it is more appropriate to have this function return true and false inside Maple.

Because not is a Maple keyword, it must be surrounded with back-tick name quotes.

$\mathrm{MapleTA}:-\mathrm{Builtin}:-\mathrm{`not`}\left(1<2\right)$

$\mathrm{false}$

$\mathrm{MapleTA}:-\mathrm{Builtin}:-\mathrm{`not`}\left(2<1\right)$

$\mathrm{true}$

The MapleTA[Builtin][not] command was introduced in Maple 18.

For more information on Maple 18 changes, see Updates in Maple 18.