mathlib

125055b0 - refactor(data/sym/basic): change notation for sym.cons (#14853)

refactor(data/sym/basic): change notation for sym.cons (#14853) Switch from `::` to `::ₛ` for `sym.cons` so that it no longer conflicts with `list.cons`. This (finally) puts it in line with other notations, like `::ₘ` for `multiset.cons`.