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*Definition:*
A value `x` is a *lower bound* of `S`, if
it is less than or equal to any element of `S`:

xis lower bound ofSw.r.t.<=: <=>forallyinS:x<=y.

A value `x` is an *upper bound* of `S`, if it is greater than
or equal to any element of `S`:

xis upper bound ofSw.r.t.<=: <=>forallyinS:y<=x.

*A lower (upper) bound of a set S need
not be element of S.*

Author: Wolfgang Schreiner

Last Modification: January 18, 2000