English
The set of unique symbols in a FreeMonoid element a is the finite set of its letters, i.e., List.toFinset a.
Русский
Множество уникальных символов элемента FreeMonoid — это конечное множество его букв: List.toFinset a.
LaTeX
$$$\\mathrm{symbols}(a) = \\mathrm{List.toFinset}(a).$$$
Lean4
/-- the set of unique symbols in a free monoid element -/
@[to_additive /-- The set of unique symbols in an additive free monoid element -/
]
def symbols (a : FreeMonoid α) : Finset α :=
List.toFinset a