[en] The proof given by J. S. Bell of an inequality between mean values of measurement results which, according to him, would be characteristic of any local hidden-parameter theory, is analyzed. It is shown that Bell's proof is based upon a hypothesis already contained in von Neumann's famous theorem: It consists in the admission that hidden values of parameters must obey the same statistical laws as observed values. This hypothesis contradicts in advance well known and certainly correct statistical relations in measurement results: one must therefore reject the type of theory considered by Bell, and his inequality has no general meaning