and poly(4-hydroxybutyrate), are displayed in the inset of Fig. . Both precursors are heterocycles; however, the algorithm has identified them as cyclic monomers and assigned them to the polyether class. Consequently, the head and tail positions were incorrectly assigned as well. To improve prediction accuracy, a future version of the HTA algorithm should include a definition that cyclic precursors can generate polyester oligomers.