) A ''k''-cell
which is a Cartesian product
of half-closed interval
s which are closed at their infima
and open at their suprema
, and such that the infimum of each interval is the coordinate
of a given point (called "the corner" of the ''δ''-box), and the length (i.e., measure
) of each interval is equal to (the given value) ''δ''.