. . . "4-methylmuconolactone methylisomerase" . "4-carboxymethyl-4-methylbutenolide mutase" . "4-methyl-2-enelactone methyl-isomerase" . "4-methyl-3-enelactone methyl isomerase" . "4-carboxymethyl-4-methylbut-2-en-1,4-olide = 4-carboxymethyl-3-methylbut-2-en-1,4-olide." .