SizeScreen()
In this form SizeScreen returns the size of the screen as a list with
two entries. The first is the length of each line, the second is the
number of lines.
SizeScreen( [ x, y ] )
In this form SizeScreen sets the size of the screen. x is the length
of each line, y is the number of lines. Either value may be missing,
to leave this value unaffected. Note that those parameters can also be
Getting and Installing GAP).
GAP 3.4.4