As was previously shown for the space-time 4-vector, a similar 4-vector can be composed of momentum. Using index notation, the energy and momentum components can be combined into a single "4-vector", that has units of momentum(i.e. E/c is a distance with c=1).
As shown earlier,
Following the 4-vector of space-time for momentum-energy,
Using the relativistic equation for energy
A 4-momenta vector can be composed of different 4-momenta vectors,
This allows us to write
Using the relationship shown for 4-vectors,