 In other words, assume there is a class ω in such that for every "b", the restriction ω"b" of ω to "X""b" is a Kähler class.ω"b" determines a bilinear form "Q" on "H""k"("X""b", C) by the rule
This form varies holomorphically in "b", and consequently the image of the period mapping satisfies additional constraints which again come from the Hodge–Riemann bilinear relations.These are