(2<i>R</i>,3<i>R</i>)-1,4-Dioxaspiro[4.4]nonane-2,3-dicarboxylic and (2<i>R</i>,3<i>R</i>)-1,4-dioxaspiro[4.5]decane-2,3-dicarboxylic acids
Acta crystallographica. Section E, Crystallographic communications