Syntax:  SET MAX UNDO number

  Sets the maximum number of commands you can undo for a specific
  buffer.

  Specify the maximum number of commands you can undo in the "number".
  qualifier.  In the "buffer name" qualifier, specify the buffer for
  which you want to set the maximum number.  If you omit a value in the
  optional "number" qualifier, LSE displays a default maximum Undo
  number of [100].  Press Return to accept the default or specify a
  different value.