Lower Bounds for Pinning Lines by Balls (Extended Abstract)

International audienceIt is known that if n>=2d pairwise disjoint balls in R^d have a unique line ℓ intersecting them in a given order <, one can always remove a ball so that ℓ remains the only line intersecting the balls in the order induced by <. We show that the constant 2d is best possible, in any dimension, and derive lower bounds on Helly numbers for sets of line transversals to disjoint balls in arbitrary dimension