Upper and Lower Bounds for Kronecker Constants of Three-Element Sets of   Integers
  Various upper and lower bounds are provided for the (angular) Kronecker constants of sets of integers. Some examples are provided where the bounds are attained. It is proved that 5=16 bounds the angular Kronecker constants of 3-element sets of positive integers. However, numerous examples suggest that the minimum upper bound is 1=4 for 3-element sets of positive integers. 
L. Thomas Ramsey and Kathryn E. Hare
math.FA