The overset command does not work in lyx-1.2.0. It requires a {} after overset, however the {} is gone every single time after saving the document.
Example: In math mode, with AMS-tex on: B overset{k_1}{k_{-1}} C After saving the first {} (around k_1) are gone! I would be very glad if there was a temporary patch. Ulrich -- Ulrich Günther