Czy:
\(\displaystyle{ \mathbb{C}\left[ X,Y\right]/\left( X ^{2}-Y ^{2} \right) \simeq \mathbb{C}\left[ X,Y\right]/ \left( XY\right)}\)
\(\displaystyle{ \mathbb{Z}\left[ X\right]/\left( 2X\left( X-1\right) \right) \simeq \mathbb{Z}\left[ X\right]/ \left( X\left( X-1\right) \right)}\)
\(\displaystyle{ \mathbb{Q}\left[ X\right]/\left( 2X\left( X-1\right) \right) \simeq \mathbb{Q}\left[ X\right]/ \left( X\left( X-1\right) \right)}\)