Rabinowitsch trick (source code)

= Rabinowitsch trick
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To prove the <Strong Hilbert Nullstellensatz> from its weak form, adjoin a variable $y$ and the equation $1-yf$. If $f$ vanishes on $V(I)$, the ideal $(I,1-yf)$ has no common zero and is therefore the unit ideal. Substituting $y=f^{-1}$ and clearing denominators yields $f^N\in I$ for some $N$.