TK> I installed that instruction. It was a slight variant of the PDP-6/10 rotate combined instruction, which rotated two adjacent accumulators as a single 72 bit word. The bit reverse version shifted one accumulator right and the other left, while passing the bit across the boundary. <TK And it was called CIRCulate! Damn, I'd completely forgotten! I think Rich used it while counting the 5x5 magic squares. --rwg