Let F = GF(q) denote the finite field with q = 2n elements. For f(X) ∈ F[X] we let
A deep result of Carlitz and Uchiyama states that if f(X)≠g(X)2+g(X)+b,g(X) ∈ F[X],b ∈ F, then
This estimate is proved in an elementary way when deg f = 3,4,5 or 6. In certain cases the estimate is improved.
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