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On subsets of GF( q 2 ) with d th power differences

1999, Discrete Mathematics

Abstract

Van Lint and MacWilliams (IEEE Trans. Inform. Theory IT 24 (1978) 730-737) conjectured that the only q-subset X of GF(q 2), with the properties 0; 1 ∈ X and x − y is a square for all x; y ∈ X , is the set GF(q). Aart Blokhuis (Indag. Math. 46 (1984) 369-372) proved the conjecture for arbitrary odd q. In this paper we give a similar characterization of GF(q) in GF(q 2), proving the analogue of Blokhuis' theorem for dth powers (instead of squares), when d|(q + 1). We also prove an embedding-type result, stating that if |S| ¿ q − (1 − 1=d) √ q with the same properties as X above, then S ⊆ GF(q).