An improvement of Mach's definition of mass

Mach's definition of mass is completed and simplified. An operative definition of inertial reference frame is proposed. The second and the third law of dynamics are stated for an isolated pair of material points at rest, in a form which does not involve the concept of force. By means of the third law of dynamics, it is proved that the ratio of two masses is independent of the choice of the reference material point and can be measured directly. This proof completes Mach's definition of mass. Then, force is defined as the product of mass and acceleration. Finally, the definitions of mass and force are extended to the framework of special relativity