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Is it true that the singular locus of an irreducible hypersurface in $\mathbb{P}^3$ have pure co-dimension ?

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    $\begingroup$ The singular locus of the quartic surface $XY(X-T)^2+Z^4=0$ is the union of the line $X=T$, $Z=0$ and the point $X=Y=Z=0$. $\endgroup$
    – abx
    Commented Nov 1, 2018 at 7:00
  • $\begingroup$ However, the non-normal locus of a hypersurface has pure codimension 1. (You really just need S2 for this). $\endgroup$ Commented Nov 1, 2018 at 23:01

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