(3-Methyl-4-oxo-5-(1-piperidinyl)-2-thiazolidinylidene)acetic acid ethyl ester 2-Carbethoxymethylene-3-methyl-5-piperidino-4-thiazolidone 3-Methyl-4-oxo-5-piperidino-delta(sup 2,a)-thiazolidineacetic acid