Hi Tom, yes mirror twice like Brian says will do it, but you will have to keep the "in between" object around as well for history to work.

Another way you can do it without needing an extra object is to use the Transform > Rotate command. Select your object and run Transform > Rotate, and set the "Make copies" checkbox, and do a 180 degree rotation. Also a shortcut for setting "Make copies" is to hold down the Ctrl key when using the mouse to place points in Rotate. Then after you have finished the rotation select the new object and run Edit > History > "Enable updates" button to turn on history updates on the new piece, it's not enabled by default for Rotate's output like it is for Mirror. After that it should be set up how you want, see attached file.

- Michael