Pointwise scalar operations of sets #
This file defines pointwise scalar-flavored algebraic operations on sets.
Main declarations #
For sets s and t and scalar a:
s • t: Scalar multiplication, set of allx • ywherex ∈ sandy ∈ t.s +ᵥ t: Scalar addition, set of allx +ᵥ ywherex ∈ sandy ∈ t.s -ᵥ t: Scalar subtraction, set of allx -ᵥ ywherex ∈ sandy ∈ t.a • s: Scaling, set of alla • xwherex ∈ s.a +ᵥ s: Translation, set of alla +ᵥ xwherex ∈ s.
For α a semigroup/monoid, Set α is a semigroup/monoid.
As an unfortunate side effect, this means that n • s, where n : ℕ, is ambiguous between
pointwise scaling and repeated pointwise addition; the former has (2 : ℕ) • {1, 2} = {2, 4}, while
the latter has (2 : ℕ) • {1, 2} = {2, 3, 4}. See note [pointwise nat action].
Appropriate definitions and results are also transported to the additive theory via to_additive.
Implementation notes #
- The following expressions are considered in simp-normal form in a group:
(fun h ↦ h * g) ⁻¹' s,(fun h ↦ g * h) ⁻¹' s,(fun h ↦ h * g⁻¹) ⁻¹' s,(fun h ↦ g⁻¹ * h) ⁻¹' s,s * t,s⁻¹,(1 : Set _)(and similarly for additive variants). Expressions equal to one of these will be simplified. - We put all instances in the scope
Pointwise, so that these instances are not available by default. Note that we do not mark them as reducible (as argued by note [reducible non-instances]) since we expect the scope to be open whenever the instances are actually used (and making the instances reducible changes the behavior ofsimp.
Tags #
set multiplication, set addition, pointwise addition, pointwise multiplication, pointwise subtraction