In algebraic geometry, is the dual of the dual curve the original curve? Why or why not?
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closed as offtopic by Alexey Ustinov, abx, Myshkin, Daniel Loughran, Stefan Kohl Nov 14 '15 at 10:06
This question appears to be offtopic. The users who voted to close gave this specific reason:
 "MathOverflow is for mathematicians to ask each other questions about their research. See Math.StackExchange to ask general questions in mathematics." – Alexey Ustinov, abx, Myshkin, Daniel Loughran, Stefan Kohl

3$\begingroup$ This is a very classical result, true for hypersurfaces of any dimension; you'll find a proof in many places, including Chapter 1 of Dolgachev's book. MO is a site for questions about mathematics at research level, please consider using math.stackexchange.com instead. $\endgroup$ – abx Nov 14 '15 at 6:05

2$\begingroup$ Since the OP did not specify the ground field, I should point out that this is not always true in positive characteristic. A simple counterexample is of a conic in characteristic two. The dual is a line and the double dual a point. $\endgroup$ – Felipe Voloch Nov 14 '15 at 15:28
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This is claimed and proved as Theorem 1 here https://math.berkeley.edu/~monks/papers/DualityV3.pdf