Lean4
/-- A morphism of Lie algebras `f : L → L'` pushes forward Lie ideals of `L` to Lie ideals of `L'`.
Note that unlike `LieSubmodule.map`, we must take the `lieSpan` of the image. Mathematically
this is because although `f` makes `L'` into a Lie module over `L`, in general the `L` submodules of
`L'` are not the same as the ideals of `L'`. -/
def map : LieIdeal R L' :=
LieSubmodule.lieSpan R L' <| (I : Submodule R L).map (f : L →ₗ[R] L')