On a common law for Malus and Bell

Malus's law and the correlations of Bell-type experiments yield the same curve, the squared cosine of the angular gap between two polarizers. We show that they are the same phenomenon. A polarizer is a pair of orthogonal planes: its response is binary, exact on the axis and on the orthogonal, and the reading of a radial quantity by a plane is a projection, a cosine. A correlation between two polarizers is a double event: one projection factor per verdict, hence the square. The photon contributes only one property, x, defined by a single clause: two photons sharing x respond identically at equal angles. Malus tests x in series, on one photon that conserves it. Bell tests it in parallel, on a pair that shares it. No further hypothesis is required. The squared cosine thus belongs to the polarizer, and the correlation of Bell-type experiments receives a purely mechanical explanation.