Each double point assigned to an irreducible algebraic curve whose curve genus is nonnegative imposes exactly one condition.
Lefschetz Theorem
See also
Hard Lefschetz TheoremExplore with Wolfram|Alpha
References
Coolidge, J. L. A Treatise on Algebraic Plane Curves. New York: Dover, p. 104, 1959.Referenced on Wolfram|Alpha
Lefschetz TheoremCite this as:
Weisstein, Eric W. "Lefschetz Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LefschetzTheorem.html