Revision as of 18:34, 2 April 2019 edit D.Lazard (talk \| contribs) Extended confirmed users 35,642 edits Changing short description from "Theorem asserting that the image of a projective variety by a projection is also a variety" to "The image of a projective variety by a projection is also a variety" (Shortdesc helper) ← Previous edit		Revision as of 14:18, 17 August 2020 edit undo Whitlams (talk \| contribs) 82 edits m →A simple motivating example: fixed grammar Next edit →
Line 13: :<math>(x,y)\mapsto \pi(x,y)=x.</math> This projection is not [[closed map\|closed]] for the [[Zariski topology]] (~~as well as~~nor for the usual topology if <math>k= \R</math> or <math>k= \C</math>), because the image by <math>\pi</math> of the [[hyperbola]] {{mvar\|H}} of equation <math>xy-1=0</math> is <math>L_x\setminus \{0\},</math> which is not closed, although {{mvar\|H}} is closed, being an [[algebraic variety]].

Main theorem of elimination theory: Difference between revisions