The range of a MonoidHomWithZero #
Given a MonoidWithZeroHom
f : A → B
whose codomain B
is a MonoidWithZero
, we define the
type MonoidHomWithZero.valueMonoid
as the submonoid of Bˣ
generated by the invertible elements
in the range of f
. For example, if A = ℕ
, f
is the natural cast to B
where B
is
ℝ≥0
, thenMonoidWithZero.valueMonoid
are the positive natural numbers inℝ≥0
;WithZero ℤ
, thenMonoidWithZero.valueMonoid = {1}
.
MonoidHomWithZero.valueMonoid₀
is the MonoidWithZero
obtained by
adjoining 0
to the previous type.
Likewise, MonoidHomWithZero.valueGroup
is the subgroup of Bˣ
generated by the invertible
elements in range f
and ``MonoidHomWithZero.valueGroup₀adds a
0` to the previous group.
When B
is commutative, then both MonoidHomWithZero.valueGroup f
and
MonoidHomWithZero.valueGroup₀ f
are also commutative and the former can be described more
explicitly (see MonoidHomWithZero.mem_valueGroup_iff_of_comm
).
Main Results #
valueMonoid f
is the smallest submonoid ofBˣ
containing the range off
;valueMonoid₀ f
is the smallest submonoid with0
containing the range off
;valueGroup f
is the smallest subgroup ofBˣ
containing the range off
;valueMonoid₀ f
is the smallest subgroup with0
containing the range off
;- When
B
is a group with zero, rather than merely a monoid with zero, the above definitions all coincide: seevalueMonoid_eq_valueGroup
for an equality as submonoids andvalueMonoid_eq_valueGroup'
for an equality as subsets. - When
B
is a commutative group with zero,MonoidHomWithZero.valueGroup
can be explicitely descibed as the elements that are ratios of terms inrange f
, seeMonoidHomWithZero.mem_valueGroup_iff_of_comm
.
Implementation details #
MonoidHomWithZero.valueMonoid
is defined explicitely in terms of its carrier, by proving the
required properties; that it coincides with the submonoid generated by the closure is proven in
MonoidHomWithZero.valueMonoid_eq_closure
, but using the latter as definition yields to unwanted
unfolding.
For a morphism of monoids with zero f
, this is a smallest submonoid of the invertible
elements in the codomain containing the range of f
.
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For a morphism of monoids with zero f
, this is the smallest subgroup of the invertible
elements in the codomain containing the range of f
.
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For a morphism of monoids with zero f
, this is the smallest submonoid with zero of the
codomain containing the range of f
.
Equations
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For a morphism of monoids with zero f
, this is a smallest subgroup with zero of the
codomain containing the range of f
.
Equations
Instances For
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- One or more equations did not get rendered due to their size.