Given a bent function f(x) of n variables we introduce its positive and negative functions as the Boolean functions f~+(x) and f~-(x) whose supports are M~+={a∈(Z_2)~n|w(f{direct +}l_a)=2~(n-1)+2~(n/2-1)} and M~-={a∈(Z_2)~n|w(f{direct +} l_a)=2~(n-1)-2~(n/2-1)} respectively, where w(f{direct +}l_a) denotes the Hamming weight of the Boolean function f(x){direct +}l_a (x) and l_a(x) is the linear function defined by a∈(Z_2)~n We prove that f~+(x) and f~-(x) are bent functions. Furthermore, combining the 4 minterms of 2 variables with the positive or negative functions of 4 bent functions of n variables we obtain a bent function of n+2 variables.
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