RIYADH, Sept. 4 (Xinhua) -- Straight punches, hooks and roundhouse kicks... Two humanoid robots wearing boxing gloves and protective headgear are staging a combat demonstration in the center of the ring. Around them, a wall of smartphones rises, capturing every jab, every feint, while the crowd gasps and cheers as if watching a title fight. This is LEAP Tech Conference in the Saudi capital Riyadh, and the robot f