More accurately, let $\displaystyle A=\sum_{i=0}^{\infty}A_i$ be a finitely generated graded algebra over say $\mathbb{Q}$ but $\dim A_i=\infty$ for each $i.$ Is it possible?
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1$\begingroup$ Think about how you can generate the elements of $A_1$ if it is infinite-dimensional. $\endgroup$– Mariano Suárez-ÁlvarezCommented Oct 5, 2010 at 19:00
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$\begingroup$ This question has already been answered, so maybe it's not that important, but the title is wrong. It says "example of a not finitely generated graded algebra", when the question asks for a finitely generated graded algebra. $\endgroup$– arsmathCommented Oct 16, 2010 at 16:56
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$\begingroup$ yes, I already correct it $\endgroup$– MelaniaCommented Oct 17, 2010 at 10:23
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1 Answer
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$\mathbb Q[x,y]$ with $x$ in degree 0, and $y$ in degree 1.
If you want your generators to be in positive degrees, then what you're asking for is impossible.
answered Oct 5, 2010 at 19:05