English
The decomposition: single a (algebraMap k A b) equals algebraMap k (SkewMonoidAlgebra k G) b times of k G a.
Русский
Разложение: single a (algebraMap k A b) равно algebraMap k (SkewMonoidAlgebra k G) b умноженному на of k G a.
LaTeX
$$$ single\ a (algebraMap k A b) = algebraMap k (SkewMonoidAlgebra k G) b \cdot of k G a $$$
Lean4
theorem single_add_erase (a : α) (f : SkewMonoidAlgebra M α) : single a (f.coeff a) + f.erase a = f :=
by
apply toFinsupp_injective
rw [single, ← toFinsupp_apply, toFinsupp_add, erase_apply_toFinsupp, Finsupp.single_add_erase]