P. Halmos addressed the problem in his highly recommended paper How to write mathematics. Let me quote his advice (from the end of Section 6).
As history progresses, more and more symbols get frozen. The standard
examples are e, i and π, and, of course, 0,1,2,3,... (Who would dare
write “Let 6 be a group.”?) A few other letters are almost frozen:
many readers would fell offended if “n” were used for a complex
number, “ε” for a positive integer, and “z” for a topological space.
(A mathematician’s nightmare is a sequence nε that tends to 0 as ε
Moral: do not increase the rigid frigidity. Think
about the alphabet. It’s a nuisance, but it’s worth it. To save time
and trouble later, think about the alphabet for an hour now; then