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Let X ⊂ P N be a complex projective variety. Let \(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}\to {P} ^N\) be the projective space whose points are hyperplanes in P N . Let x ∈ X be any smooth point. A hyperplane \(H \in \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}\to {P} ^N\) is said to be tangent to X at x if H contains the tangent subspace T xX. The projective dual variety \(X^V \subset \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}\to {P} ^N\) is defined as the closure of the locus of those hyperplanes H which are tangent to X in some smooth point, see [7]. The name “projective dual” is justified by the biduality theorem [7]: the dual to X⋁ coincides with X.