Dear Sir: I just ran across your exchange of ideas on FeCo order etc. about this time last year. I did some experiments in the mid 60s (Trans. Met. Soc AIME 236 (1966) 14ff.) on FeCo2V and showed that the superlattice xray line [100} can be seen in brine-quenched thin strips if the XRD is done with CoKa radiation. The lines are very broad in as-quenched state and the peak narrows gradually with time of reheating to a few hundred degrees C. The interpretation was that we were seeing APB domains which were unexpected but seemed obvious in hindsight--two interpenetrating, multiply-connected domains sort of like "swiss cheese" (J. W. Cahn called it "sponge" at the time--he wrote an elegant mathematical analysis that appeared in Acta Met.). The "scale" of interconnection changes with time at temperature as the structure coarsens to reduce the energy associated with APB. I thought the picture was confusing since "perfect order with very fine domain size" could as well be described as partial, or incomplete order due to large number of wrong near neighbors. I don't know if there are other alloys or chemical combinations in which B2 order is present with very fine domain structure such as I described. I am not aware of any other work that confirmed or reinterpreted my results. Any comments? Alan English Summit NJ