Until fairly recently, 3 wire range circuits were allowed under certain conditions, in such a circuit the same conductor serves as both the neutral and the equipment ground.
Existing installations may continue in use. 3 pin outlets and 3 core flex being used, with a jumper wire within the appliance that connects together the equipment ground and the neutral.
All new range circuits are required to be 4 wire with 4 pin outlets and 4 core flex, the neutral and equipment ground being seperate throughout.
No neutral/equipment ground jumper should be used within the appliance if it is served by a 4 wire circuit.