The proof of the weak Nullstellensatz in Qing Liu’s bookProof of Hilbert's NullstellensatzA proof of the Noether Normalization LemmaI need help in this proof in Lang's algebra bookQuotient of ring is flat gives an identity of idealsTheorem 1 in chapter II.4 of Mumford's Red BookAtiyah-MacDonald: proof of Proposition 7.9, weak Nullstellensatz.Lemma 4.1.7. in Bruns and Herzog, Cohen-Macaulay Ringsa proof in Matsumura's bookweak Bezout's theorem proofHilbert Nullstellensatz, Eisenbud's proof

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The proof of the weak Nullstellensatz in Qing Liu’s book


Proof of Hilbert's NullstellensatzA proof of the Noether Normalization LemmaI need help in this proof in Lang's algebra bookQuotient of ring is flat gives an identity of idealsTheorem 1 in chapter II.4 of Mumford's Red BookAtiyah-MacDonald: proof of Proposition 7.9, weak Nullstellensatz.Lemma 4.1.7. in Bruns and Herzog, Cohen-Macaulay Ringsa proof in Matsumura's bookweak Bezout's theorem proofHilbert Nullstellensatz, Eisenbud's proof













0












$begingroup$


I am reading Qing Liu’s book and the whole proof on pp 30 goes like this:




enter image description here




I do not understand the conclusion in the yellow-highlighted line. Let $f$ be the isomorphism highlighted in red. Why $f$ maps $alpha_i$ to $alpha_i$?










share|cite|improve this question











$endgroup$
















    0












    $begingroup$


    I am reading Qing Liu’s book and the whole proof on pp 30 goes like this:




    enter image description here




    I do not understand the conclusion in the yellow-highlighted line. Let $f$ be the isomorphism highlighted in red. Why $f$ maps $alpha_i$ to $alpha_i$?










    share|cite|improve this question











    $endgroup$














      0












      0








      0





      $begingroup$


      I am reading Qing Liu’s book and the whole proof on pp 30 goes like this:




      enter image description here




      I do not understand the conclusion in the yellow-highlighted line. Let $f$ be the isomorphism highlighted in red. Why $f$ maps $alpha_i$ to $alpha_i$?










      share|cite|improve this question











      $endgroup$




      I am reading Qing Liu’s book and the whole proof on pp 30 goes like this:




      enter image description here




      I do not understand the conclusion in the yellow-highlighted line. Let $f$ be the isomorphism highlighted in red. Why $f$ maps $alpha_i$ to $alpha_i$?







      commutative-algebra






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited 2 days ago







      user150248

















      asked 2 days ago









      user150248user150248

      346110




      346110




















          1 Answer
          1






          active

          oldest

          votes


















          0












          $begingroup$

          These corollaries (explicitly) talk about $k$-algebras, so every morphism is $k$-linear. This implies that $f(alpha_i)=alpha_i+mathfrakm$.



          In the category of $k$-algebras $k$ is an initial object, so for any $k$-algebra $A$ there is exactly one $k$-algebra homomorphism $gcolon kto A$. This must be a ring morphism, so $g(1)=1_A$. And it must be $k$-linear, so $g(alpha)=alpha cdot 1_A$.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
            $endgroup$
            – user150248
            2 days ago










          • $begingroup$
            Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
            $endgroup$
            – user150248
            2 days ago










          Your Answer





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          1 Answer
          1






          active

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          active

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          active

          oldest

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          0












          $begingroup$

          These corollaries (explicitly) talk about $k$-algebras, so every morphism is $k$-linear. This implies that $f(alpha_i)=alpha_i+mathfrakm$.



          In the category of $k$-algebras $k$ is an initial object, so for any $k$-algebra $A$ there is exactly one $k$-algebra homomorphism $gcolon kto A$. This must be a ring morphism, so $g(1)=1_A$. And it must be $k$-linear, so $g(alpha)=alpha cdot 1_A$.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
            $endgroup$
            – user150248
            2 days ago










          • $begingroup$
            Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
            $endgroup$
            – user150248
            2 days ago















          0












          $begingroup$

          These corollaries (explicitly) talk about $k$-algebras, so every morphism is $k$-linear. This implies that $f(alpha_i)=alpha_i+mathfrakm$.



          In the category of $k$-algebras $k$ is an initial object, so for any $k$-algebra $A$ there is exactly one $k$-algebra homomorphism $gcolon kto A$. This must be a ring morphism, so $g(1)=1_A$. And it must be $k$-linear, so $g(alpha)=alpha cdot 1_A$.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
            $endgroup$
            – user150248
            2 days ago










          • $begingroup$
            Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
            $endgroup$
            – user150248
            2 days ago













          0












          0








          0





          $begingroup$

          These corollaries (explicitly) talk about $k$-algebras, so every morphism is $k$-linear. This implies that $f(alpha_i)=alpha_i+mathfrakm$.



          In the category of $k$-algebras $k$ is an initial object, so for any $k$-algebra $A$ there is exactly one $k$-algebra homomorphism $gcolon kto A$. This must be a ring morphism, so $g(1)=1_A$. And it must be $k$-linear, so $g(alpha)=alpha cdot 1_A$.






          share|cite|improve this answer









          $endgroup$



          These corollaries (explicitly) talk about $k$-algebras, so every morphism is $k$-linear. This implies that $f(alpha_i)=alpha_i+mathfrakm$.



          In the category of $k$-algebras $k$ is an initial object, so for any $k$-algebra $A$ there is exactly one $k$-algebra homomorphism $gcolon kto A$. This must be a ring morphism, so $g(1)=1_A$. And it must be $k$-linear, so $g(alpha)=alpha cdot 1_A$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 2 days ago









          PedroPedro

          2,9291720




          2,9291720











          • $begingroup$
            It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
            $endgroup$
            – user150248
            2 days ago










          • $begingroup$
            Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
            $endgroup$
            – user150248
            2 days ago
















          • $begingroup$
            It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
            $endgroup$
            – user150248
            2 days ago










          • $begingroup$
            Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
            $endgroup$
            – user150248
            2 days ago















          $begingroup$
          It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
          $endgroup$
          – user150248
          2 days ago




          $begingroup$
          It may not be $k$-linear in the desired way. Perhaps $f^-1$ maps all the scalar elements to a proper subfield of $k$.
          $endgroup$
          – user150248
          2 days ago












          $begingroup$
          Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
          $endgroup$
          – user150248
          2 days ago




          $begingroup$
          Oh I think I get it. Qing has been always talking about k-algebra homomorphisms since the proof of the normalization lemma, although he did not give any definition of “finite homomorphism”.
          $endgroup$
          – user150248
          2 days ago

















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