I need to write down a complicated proof for a paper, for which I need to employ equations that I established earlier for almost every new relation I show. I would consider it best for the reader, if I denoted the number of the employed relations to establish a new relation over each relation sign.
In a simplified example, I would like to write something like: $$ x+y-z \stackrel{3.1}{=} x+w, $$ where equation 3.1 gives me $y-z=w$.
However, I cannot remember seeing this or a similar notation in the mathematical literature, which may be for a good reason. My question therefore is: Is there any such good reason against writing down proofs like this or have I just been reading the wrong papers?
Also, should such a reason exist: What would be similar, acceptable ways to write this down? I would strongly dislike writing a sentence about the employed relations for every single relation I show, as this would make the proof very hard to follow in my opinion. (Leaving finding the employed relations as an exercise to the reader is not an option, given the vast amount of relations.)
The way I've seen it is to put numbers before or after the equations in parentheses with colons, like so:
$$3 + x = 1$$
$$\implies x = - 2 \quad :(1)$$
Let $t = -x$. Then:
$$(2):\quad t = 2 \quad \text{by (1)}$$
It follows that:
$$(3): \quad x + t = 0 \quad \text{by (1) and (2)}$$