  An ensemble consisting on systems of two entangled spin 1/2 particles, all of
them in the same global quantum state, are considered. The two spins are
measured, each of them, on a fixed direction, at two randomly selected
measurement times. Realism, plus locality and freedom of choice referred to
these chosen times, are assumed. Then, from the sole correlation function
related to the two measurements, without considering any Bell inequalities, a
contradiction between these assumptions and quantum mechanics is found.
