IMO 1979 LL VIE72

Let f(x) be a polynomial with integer coefficients. Prove that

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IMO 1979 LL VIE72

Origin: VIE

Problem

Let f(x) be a polynomial with integer coefficients. Prove that if f(x) equals 1979 for four different integer values of x, then f(x) cannot be equal to 2 \times 1979 for any integral value of x.