Paragraph: P and Q are isomers of dicarboxylic acid C_ 4 H_ 4 O_ 4...

Paragraph: $P$ and $Q$ are isomers of dicarboxylic acid $\mathrm{C}_{4} \mathrm{H}_{4} \mathrm{O}_{4}$. Both decolorize $\mathrm{Br}_{2} / \mathrm{H}_{2} \mathrm{O}$. On heating, $\boldsymbol{P}$ forms the cyclic anhydride. Upon treatment with dilute alkaline $\mathrm{KMnO}_{4}, \boldsymbol{P}$ as well as $\boldsymbol{Q}$ could produce one or more than one from $\boldsymbol{S}, \boldsymbol{T}$ and $\boldsymbol{U}$.



Question: Compounds formed from $\boldsymbol{P}$ and $\boldsymbol{Q}$ are, respectively