Eberhard's theorem

Eberhard's theorem is a result in the field of projective geometry, specifically concerning sets of points and their configurations. The theorem states that if a finite set \( S \) of points in the projective plane is such that every line intersects at least \( \lambda \) points of \( S \), then the total number of points in \( S \) is at most \( \lambda^2 \).