A class of reversible cubic systems with an isochronous center

We study cubic polynomial differential systems having an isochronous center and an inverse integrating factor formed by two different parallel invariant straight lines. Such systems are time-reversible. We find nine subclasses of such cubic systems, see Theorem 8. We also prove that time-reversible polynomial differential systems with a nondegenerate center have half of the isochronous constants equal to zero, see Theorem 3. We present two open problems.