It's standard practice for mathematics papers. Some people like to view it as "we, the author and the reader".

A form of "plural majestatis" which paradoxically implies that the individual author has only relative importance

(«paradoxically» as the majestas itself is founded on representing something higher, not of some high status of the individual which happens to be endowed - it may sound like boasting but on the contrary it would be a downplay of the individual).

In other contexts, that "we" can have even more foundations: "I could never have done this without the work of others", "Not just me but all those who think alike" etc.

Using the "royal we" is standard in mathematics. If you ever see someone do this in ordinary writing you can bump up your odds that they're a mathematician. Another giveaway is using "modulo" to mean "except for".

It's the "royal 'we'"

me and cockroaches in my head