To take up a slightly more complex example, but one that remains simple enough to pursue through a complete series of developments, consider the transformation from ''U''<sup> •</sup> = [''u'', ''v''] to ''X''<sup> •</sup> = [''x'', ''y''] that is defined by the following system of equations: | To take up a slightly more complex example, but one that remains simple enough to pursue through a complete series of developments, consider the transformation from ''U''<sup> •</sup> = [''u'', ''v''] to ''X''<sup> •</sup> = [''x'', ''y''] that is defined by the following system of equations: |