Assume that J is a set of intervals on the real line. The following
two important minimax theorems have been discovered by Tibor Gallai.
1. minimum number of partition classes of J into pairwise disjoint
intervals = maximum number of pairwise intersecting members of J
2. minimum number of points piercing all members of J = maximum number
of pairwise disjoint members of J
What happens if J is replaced by other structures? By subtrees of a
tree? By arcs of a circle? By boxes? By intervals of the plane?