[MrManatee]

Yeah, I suppose this would be acceptable in this instance. But it still repeats x and y, and if x and y were complicated expressions instead of just simple variables, I wouldn't want to repeat them.

For example, the proof of the Minkowski inequality in Wikipedia [1] contains a statement of the form "x_1 = x_2 = x_3 ≤ x_4 = x_5 ≤ x_6 = x_7". Except that x_1, ..., x_7 are so complicated that any notation that requires repeating them doesn't feel like a satisfactory notation for "all of mathematics".

[1] https://en.wikipedia.org/wiki/Minkowski_inequality