Explore a complex algebraic geometry problem in this lecture by Claire Voisin at Institut Henri Poincaré. Delve into the Whitney embedding theorem in differential geometry and its relation to a question posed by Borel and Haefliger in complex algebraic geometry. Examine whether the cohomology class of an algebraic subvariety in a smooth projective variety can be expressed as a combination of classes of smooth subvarieties with integral coefficients. Learn about classical and recent results on this topic, with a focus on the Whitney range, which has been recently solved affirmatively by Kollár and Voisin.