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

Hey thank you Bem and David for your replies ! What I did until
now to achieve the inverse symmetry was the way Bem suggested.
Problem : I have to keep the first mirrored object and even when I hide it
it will pop up each time I change the original. So to rotate the object
and activate history will solve my problem. Back to modelling - never
had a tool which translates inspiration so fast and effortlessly into shape as MOI.
And more than once during work it slips put form me : Damn, this mind behind
MOI is a true dedicated master of his genre ! Such a pleasure to discover so many
little intelligent features which help the creative flow manifest almost immediately
onscren. Ther couldmot be a better name than "Moments of Inspiration" - for the
time spent with this tool ;-)

Thanks very much Tom, I'm glad that MoI is working well for you!

- Michael

Actually its like tailor-made for my current needs ;-) !