Understanding the proof of Cartier duality











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I'm trying to understand the above proof of Cartier Duality.



The step I don't understand is the following



It says



$$ phipsi(a) = ((phi otimes psi) circ Delta(a) = (phi otimes psi)( a otimes a) $$ for all $f,g$



Why does it implies $Delta(a) = a otimes a$?



It may possible that $operatorname{ker}(phi otimes psi)$ is not trivial for all $phi$ and $psi$.



Here the $Delta$ is the co-multiplication map of the Hopf algebra $A$.










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  • Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
    – random123
    Nov 22 at 7:02

















up vote
0
down vote

favorite












enter image description here



I'm trying to understand the above proof of Cartier Duality.



The step I don't understand is the following



It says



$$ phipsi(a) = ((phi otimes psi) circ Delta(a) = (phi otimes psi)( a otimes a) $$ for all $f,g$



Why does it implies $Delta(a) = a otimes a$?



It may possible that $operatorname{ker}(phi otimes psi)$ is not trivial for all $phi$ and $psi$.



Here the $Delta$ is the co-multiplication map of the Hopf algebra $A$.










share|cite|improve this question






















  • Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
    – random123
    Nov 22 at 7:02















up vote
0
down vote

favorite









up vote
0
down vote

favorite











enter image description here



I'm trying to understand the above proof of Cartier Duality.



The step I don't understand is the following



It says



$$ phipsi(a) = ((phi otimes psi) circ Delta(a) = (phi otimes psi)( a otimes a) $$ for all $f,g$



Why does it implies $Delta(a) = a otimes a$?



It may possible that $operatorname{ker}(phi otimes psi)$ is not trivial for all $phi$ and $psi$.



Here the $Delta$ is the co-multiplication map of the Hopf algebra $A$.










share|cite|improve this question













enter image description here



I'm trying to understand the above proof of Cartier Duality.



The step I don't understand is the following



It says



$$ phipsi(a) = ((phi otimes psi) circ Delta(a) = (phi otimes psi)( a otimes a) $$ for all $f,g$



Why does it implies $Delta(a) = a otimes a$?



It may possible that $operatorname{ker}(phi otimes psi)$ is not trivial for all $phi$ and $psi$.



Here the $Delta$ is the co-multiplication map of the Hopf algebra $A$.







algebraic-geometry commutative-algebra hopf-algebras group-schemes






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asked Nov 22 at 4:46









grok

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  • Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
    – random123
    Nov 22 at 7:02




















  • Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
    – random123
    Nov 22 at 7:02


















Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
– random123
Nov 22 at 7:02






Somehow it seems transparent to prove that $G(R) cong Hom(G^{check{}}, mathbb{G}_m)$, and then use the statement for $G^{check{}}$. Atleast that's what they is done in Algebraic Geometry - II Mumford Oda.
– random123
Nov 22 at 7:02

















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