Let $(\Omega,d)$ be a differential calculus over an algebra $A$. As It is well know, easy to show that $\Omega$ is always equal to a quotient of $\Omega_u$ \Omega_u(A)$, the universal calculus over $A$. A$, by some ideal $N$ of $\Omega_u(A)$. Now in practical terms, given a presentation of $\Omega$ in terms of generators and relations, how does one find the corresponding ideal ? $N$? I have some confused memory of there being a concrete recipe (due to Woronowicz?) for doing this when $A$ is a Hopf algebra and the calculus is left-covariant (or bi-covariant).
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Finding the Universal Ideal of a (Covariant) Differential CalculusLet $(\Omega,d)$ be a differential calculus over an algebra $A$. As is well know, $\Omega$ is equal to a quotient of $\Omega_u$ the universal calculus over $A$. Now in practical terms, given a presentation of $\Omega$ in terms of generators and relations, how does one find the corresponding ideal? I have some confused memory of there being a concrete recipe (due to Woronowicz?) for doing this when $A$ is a Hopf algebra and the calculus is left-covariant (or bi-covariant).
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