SOLUTION:
An augmenting set E' for G, i.e., a set E' of unordered
pairs of vertices from V, such that
has diameter D, i.e., the maximum distance of any pair of vertices is
at most D.
MEASURE:
Cardinality of the augmenting set, i.e., .
Bad News:
As hard to approximate as MINIMUM SET COVER [355].
Comment:
Variation in which the size of the augmenting set is bounded by D and
the problem is to minimize the diameter is approximable within
[355].