It follows that if n is much larger than f .r /, then every n-element point set P contains
many r -tuples in convex position. For instance, Solymosi [S] showed that for a suitable
constant cr > 0, we can select a sequence of crn distinct elements from P, whose any
r consecutive members are in convex position. In the case r D 4, Nielsen [N] and, in
general, B´ar´any and Valtr [BV] proved the following stronger result: