Space-time interval (2)

The notion of space-time interval should be abandoned because it is complex and leads to nothing, except final errors.
What is the space-time interval?
A metric, measured in meters.
It is mostly an abstract thing that is not very useful.
So we set ds²=dl²-c²t².
Why and for WHAT?
For nothing.
For fun.
Hachel notation is much more practical, because it does not need the notion of complexes to establish a perfect Pythagoreanism.
Hachel does not speak, because he is an immense genius, of the notion of space-time interval, ridiculous and abstract, and he does not use meters, but seconds. That is to say the units of TIME.
This is much more practical because from the invariance of ds, which we always wonder what it is, and what it can represent in nature, Hachel goes to the invariance of proper times. It is much simpler and more practical. A proper time is always invariant because it is a tautology, a truism.
Hachel then poses Tr²=To²-Et² and speaks in seconds, where physicists stupidly pose -ds²=-To².c²+dl² and speak in meters.
Finally, what is ds²? It is just -c².Tr²
Let's pose Tr²=-ds².c² and everything becomes much simpler and much more practical.
To²=Tr²+Et²
Pythagoreanism is perfect.
In plain language: In a frame of reference, the square of the observable time is equal to the square of the proper time of the mobile implemented by the square
of the anisochrony taken into account.
Practical example:
A terrestrial observer in a rocket that will travel for 15 years at 0.8c. He will therefore age 15 years.
Will the person in the rocket also age 15 years?
We set To²=Tr²+Et²
Hence Tr²=To²-Et²=15²-12²=81
Tr=9 years.
Simplicity is disconcerting.
In general, we don't like it too much.
R.H.