Physlib

Physlib.Mathematics.LinearPMap

LinearPMap

i. Overview

In this module we collect some basic results about `LinearPMap`s.

Most important is the definition of restricted composition. The composition of two partial linear maps `g : F →ₗ.[R] G` and `f : E →ₗ.[R] F` is defined only if the range of `f` is contained in the domain of `g` (c.f. `LinearPMap.comp`). `g.compRestricted f` (`g ∘ᵣ f`) is defined to be the composition of `g` with the restriction of `f` to exactly those `x : f.domain` for which `f x ∈ g.domain`. This allows one to work with the composition of partial linear maps while having the domain implicitly accounted for.

ii. Key results

- `LinearPMap.sum` : The finite sum of partial linear maps. - `LinearPMap.compRestricted` (`∘ᵣ`) : For two partial linear maps `g : F →ₗ[R] G` and `f : E →ₗ[R] F`, the composition of `g` with `f` with natural domain `{x : f.domain | f x ∈ g.domain}`. - `LinearPMap.instMonoid` : Partial linear maps `E →ₗ.[R] E` with `compRestricted` for multiplication and the identity map for `1` comprise a monoid.

iii. Table of contents

  • A. Inequalities
  • B. Zero smul
  • C. Finite sums
  • D. Restricted composition
  • E. Monoid
  • F. Inverses

iv. References

A. Inequalities

B. Zero smul

C. Finite sums

D. Restricted composition

E. Monoid

Partial linear maps `E →ₗ.[R] E` with `compRestricted` for multiplication and the identity map (domain `⊤`) for `1` comprise a monoid.

F. Inverses

55 declarations

theorem

ff0f - f \leq 0 for partial linear maps

For any partial linear map ff, the difference of ff with itself is less than or equal to the zero partial linear map, i.e., ff0f - f \leq 0. In the context of partial linear maps, the inequality ghg \leq h means that the domain of gg is a subspace of the domain of hh and that gg and hh coincide on the domain of gg.

theorem

f+f0-f + f \leq 0 for partial linear maps

For any partial linear map ff, the sum of its negation f-f and itself is less than or equal to the zero partial linear map, denoted as f+f0-f + f \leq 0. In this context, the relation ghg \leq h indicates that hh is an extension of gg (i.e., the domain of gg is a subspace of the domain of hh, and they coincide on the domain of gg).

theorem

g1g2    g1g2g_1 \le g_2 \iff -g_1 \le -g_2 for partial linear maps

For any two partial linear maps g1g_1 and g2g_2, the relation g1g2g_1 \le g_2 holds if and only if g1g2-g_1 \le -g_2. Here, the relation \le denotes the extension of partial maps, where g1g2g_1 \le g_2 means that the domain of g1g_1 is a subspace of the domain of g2g_2 and the maps agree on the domain of g1g_1.

theorem

g1g2    g1g2g_1 \le -g_2 \iff -g_1 \le g_2

For any two partial linear maps g1g_1 and g2g_2, the relation g1g2g_1 \le -g_2 holds if and only if g1g2-g_1 \le g_2 holds. Here, the inequality fgf \le g denotes that the partial linear map gg is an extension of ff, and g-g denotes the pointwise negation of the map.

theorem

f1+(f2f1)f2f_1 + (f_2 - f_1) \le f_2 for Partial Linear Maps

For any two partial linear maps f1f_1 and f2f_2, the inequality f1+(f2f1)f2f_1 + (f_2 - f_1) \le f_2 holds. In this context, for partial linear maps gg and ff, the relation gfg \le f signifies that the domain of gg is a subspace of the domain of ff and gg coincides with ff on the domain of gg. The operations of addition and subtraction for partial linear maps are defined on the intersection of the domains of the operands.

theorem

f1+f2f1f2f_1 + f_2 - f_1 \le f_2 for partial linear maps

For any partial linear maps f1f_1 and f2f_2, the inequality f1+f2f1f2f_1 + f_2 - f_1 \le f_2 holds. Here, the inequality ghg \le h for partial linear maps denotes that the domain of gg is a subspace of the domain of hh and the two maps agree on the domain of gg.

theorem

f1+f2f2f1f_1 + f_2 - f_2 \leq f_1 for partial linear maps

For any partial linear maps f1f_1 and f2f_2, it holds that f1+f2f2f1f_1 + f_2 - f_2 \leq f_1. In this context, the inequality fgf \leq g denotes that gg is an extension of ff, meaning the domain of ff is a subspace of the domain of gg and f(x)=g(x)f(x) = g(x) for all xx in the domain of ff.

theorem

f1+f2+(f3f2)f1+f3f_1 + f_2 + (f_3 - f_2) \le f_1 + f_3 for partial linear maps

For partial linear maps f1,f2,f3f_1, f_2, f_3, the inequality f1+f2+(f3f2)f1+f3f_1 + f_2 + (f_3 - f_2) \leq f_1 + f_3 holds. In the context of partial linear maps, fgf \leq g means that gg is an extension of ff (i.e., the domain of ff is a subset of the domain of gg and the maps agree on the domain of ff).

theorem

f1+f2(f1f3)f2+f3f_1 + f_2 - (f_1 - f_3) \le f_2 + f_3 for partial linear maps

For any partial linear maps f1,f2,f_1, f_2, and f3f_3, the following inequality holds: f1+f2(f1f3)f2+f3f_1 + f_2 - (f_1 - f_3) \le f_2 + f_3 where the inequality fgf \le g denotes that gg is an extension of ff (i.e., the domain of ff is a subspace of the domain of gg, and f(x)=g(x)f(x) = g(x) for all xx in the domain of ff).

theorem

(f1f2)(f3f2)f1f3(f_1 - f_2) - (f_3 - f_2) \leq f_1 - f_3 for partial linear maps

For any three partial linear maps f1,f2,f_1, f_2, and f3f_3, it holds that (f1f2)(f3f2)f1f3(f_1 - f_2) - (f_3 - f_2) \leq f_1 - f_3. Here, the relation fgf \leq g between partial linear maps signifies that the domain of ff is a subspace of the domain of gg and that f(x)=g(x)f(x) = g(x) for all xx in the domain of ff.

theorem

Left cancellation in nested subtractions (f1f2)(f1f3)f3f2(f_1 - f_2) - (f_1 - f_3) \le f_3 - f_2 for partial linear maps

For any partial linear maps f1f_1, f2f_2, and f3f_3, the following inequality holds: (f1f2)(f1f3)f3f2(f_1 - f_2) - (f_1 - f_3) \leq f_3 - f_2 where the subtraction fgf - g of two partial linear maps is defined on the intersection of their domains, and the relation fgf \leq g denotes that ff is a restriction of gg (i.e., the domain of ff is a subspace of the domain of gg and the maps agree on the domain of ff).

theorem

gg1+g2    gg2g1g \le g_1 + g_2 \implies g - g_2 \le g_1 for partial linear maps

Let g,g1g, g_1, and g2g_2 be partial linear maps. If gg1+g2g \le g_1 + g_2, then gg2g1g - g_2 \le g_1. Here, the inequality fhf \le h between partial linear maps indicates that the domain of ff is a subspace of the domain of hh and the maps coincide on the domain of ff.

theorem

f1f2+f2f1f_1 - f_2 + f_2 \le f_1 for partial linear maps

For any partial linear maps f1f_1 and f2f_2, the partial linear map f1f2+f2f_1 - f_2 + f_2 is a restriction of f1f_1, expressed as f1f2+f2f1f_1 - f_2 + f_2 \leq f_1.

theorem

gg1g2    g+g2g1g \le g_1 - g_2 \implies g + g_2 \le g_1 for partial linear maps

For any partial linear maps g,g1g, g_1, and g2g_2, if gg1g2g \le g_1 - g_2, then g+g2g1g + g_2 \le g_1. (Here, the relation \le for partial linear maps denotes that the domain of the smaller map is a subspace of the domain of the larger map, and the maps coincide on the smaller domain).

theorem

g1g2    f+g1f+g2g_1 \le g_2 \implies f + g_1 \le f + g_2 for partial linear maps

Let f,g1,f, g_1, and g2g_2 be partial linear maps. If g1g2g_1 \le g_2, then f+g1f+g2f + g_1 \le f + g_2. The relation g1g2g_1 \le g_2 for partial linear maps signifies that the domain of g1g_1 is a subspace of the domain of g2g_2 and the maps agree on the domain of g1g_1.

theorem

g1g2    g1+fg2+fg_1 \le g_2 \implies g_1 + f \le g_2 + f for partial linear maps

Let g1g_1, g2g_2, and ff be partial linear maps. If g1g2g_1 \le g_2 (meaning the domain of g1g_1 is contained in the domain of g2g_2 and g2g_2 agrees with g1g_1 on the domain of g1g_1), then g1+fg2+fg_1 + f \le g_2 + f.

theorem

g1g2    g1fg2fg_1 \le g_2 \implies g_1 - f \le g_2 - f for partial linear maps

For any partial linear maps g1g_1, g2g_2, and ff, if g1g2g_1 \le g_2, then g1fg2fg_1 - f \le g_2 - f. Here, the relation g1g2g_1 \le g_2 means that the domain of g1g_1 is a subspace of the domain of g2g_2 and g1g_1 is the restriction of g2g_2 to the domain of g1g_1.

theorem

g1g2    fg1fg2g_1 \le g_2 \implies f - g_1 \le f - g_2

For any partial linear maps ff, g1g_1, and g2g_2, if g1g2g_1 \leq g_2, then fg1fg2f - g_1 \leq f - g_2. Here, the relation g1g2g_1 \leq g_2 means that g2g_2 is an extension of g1g_1; that is, the domain of g1g_1 is a subspace of the domain of g2g_2 and g1(x)=g2(x)g_1(x) = g_2(x) for all xx in the domain of g1g_1.

theorem

(0:k)f0(0 : \mathbb{k}) \cdot f \leq 0 for partial linear maps

For any partial linear map f:EFf : E \to F over a scalar field k\mathbb{k}, the scalar product of 00 and ff is less than or equal to the zero partial linear map: (0:k)f0(0 : \mathbb{k}) \cdot f \leq 0 In the context of partial linear maps, the relation ghg \leq h means that the domain of gg is a subspace of the domain of hh and gg agrees with hh on that subspace.

theorem

0f=00 \cdot f = 0 for partial linear maps with full domain

Let ff be a partial linear map from EE to FF over a field k\mathbb{k}. If the domain of ff is the entire space EE (denoted by \top), then the scalar multiplication of ff by 0k0 \in \mathbb{k} is equal to the zero partial linear map. That is, 0f=00 \cdot f = 0.

definition

Finite sum of partial linear maps fa\sum f_a

Given a finite family of partial linear maps {fa}aα\{f_a\}_{a \in \alpha} from a module EE to FF over a ring RR, the sum aαfa\sum_{a \in \alpha} f_a is a partial linear map EFE \to F. Its domain is defined as the intersection of the domains of all maps in the family, aαdom(fa)\bigcap_{a \in \alpha} \text{dom}(f_a). The value of the sum at an element xx in this intersection is the sum of the values of each individual partial linear map, (aαfa)(x)=aαfa(x)(\sum_{a \in \alpha} f_a)(x) = \sum_{a \in \alpha} f_a(x).

theorem

dom(fa)=dom(fa)\text{dom}(\sum f_a) = \bigcap \text{dom}(f_a) for partial linear maps

For a finite family of partial linear maps {fa}aα\{f_a\}_{a \in \alpha}, the domain of their sum aαfa\sum_{a \in \alpha} f_a is the intersection of the domains of the individual maps faf_a. In mathematical notation, this is expressed as dom(aαfa)=aαdom(fa)\text{dom}(\sum_{a \in \alpha} f_a) = \bigcap_{a \in \alpha} \text{dom}(f_a).

theorem

dom(fi)dom(fa)\text{dom}(\sum f_i) \subseteq \text{dom}(f_a)

Given a finite family of partial linear maps {fi}iα\{f_i\}_{i \in \alpha}, the domain of their sum iαfi\sum_{i \in \alpha} f_i is a submodule of the domain of each individual map faf_a for any aαa \in \alpha.

theorem

(fa)(ψ)=fa(ψ)(\sum f_a)(\psi) = \sum f_a(\psi) for partial linear maps

For a finite family of partial linear maps {fa}aα\{f_a\}_{a \in \alpha} and an element ψ\psi belonging to the domain of their sum aαfa\sum_{a \in \alpha} f_a, the value of the sum evaluated at ψ\psi is the sum of each map evaluated at ψ\psi: (aαfa)(ψ)=aαfa(ψ). \left(\sum_{a \in \alpha} f_a\right)(\psi) = \sum_{a \in \alpha} f_a(\psi). Note that ψ\psi belongs to the domain of the sum if and only if it belongs to the intersection of the domains of all individual maps faf_a.

definition

Restricted composition grfg \circ_r f of partial linear maps

Given partial linear maps f:EFf: E \to F and g:FGg: F \to G with domains dom(f)E\text{dom}(f) \subseteq E and dom(g)F\text{dom}(g) \subseteq F respectively, their restricted composition grfg \circ_r f is the partial linear map from EE to GG whose domain consists of those xdom(f)x \in \text{dom}(f) such that f(x)dom(g)f(x) \in \text{dom}(g). For such xx, the value is defined as (grf)(x)=g(f(x))(g \circ_r f)(x) = g(f(x)).

definition

Restricted composition notation r\circ_r for partial linear maps

The notation grfg \circ_r f denotes the restricted composition of two partial linear maps ff and gg. If ff is a partial linear map from EE to FF and gg is a partial linear map from FF to GG, then grfg \circ_r f is defined as the partial linear map whose domain consists of those xx in the domain of ff for which f(x)f(x) is in the domain of gg. The mapping is given by (grf)(x)=g(f(x))(g \circ_r f)(x) = g(f(x)).

theorem

dom(grf)dom(f)\text{dom}(g \circ_r f) \subseteq \text{dom}(f)

Let f:EFf: E \to F and g:FGg: F \to G be partial linear maps. The domain of their restricted composition grfg \circ_r f is contained in the domain of ff, which is expressed as dom(grf)dom(f)\text{dom}(g \circ_r f) \subseteq \text{dom}(f).

theorem

Domain of grfg \circ_r f equals the inclusion of the preimage of dom(g)\text{dom}(g) under ff

Let f:EFf: E \to F and g:FGg: F \to G be partial linear maps with domains dom(f)E\text{dom}(f) \subseteq E and dom(g)F\text{dom}(g) \subseteq F. Let ffun:dom(f)Ff_{\text{fun}}: \text{dom}(f) \to F denote the linear map underlying ff, and let ι:dom(f)E\iota: \text{dom}(f) \to E be the inclusion map. The domain of the restricted composition grfg \circ_r f is the image under ι\iota of the preimage of dom(g)\text{dom}(g) under ffunf_{\text{fun}}: dom(grf)=ι(ffun1(dom(g))). \text{dom}(g \circ_r f) = \iota(f_{\text{fun}}^{-1}(\text{dom}(g))).

theorem

xdom(vru)    xdom(u) and u(x)dom(v)x \in \text{dom}(v \circ_r u) \iff x \in \text{dom}(u) \text{ and } u(x) \in \text{dom}(v)

Let u:EFu: E \to F and v:FGv: F \to G be partial linear maps. For any element xEx \in E, xx belongs to the domain of the restricted composition vruv \circ_r u if and only if xx belongs to the domain of uu and its image u(x)u(x) belongs to the domain of vv.

theorem

xdom(vru)    xdom(u)u(x)dom(v)x \in \text{dom}(v \circ_r u) \iff x \in \text{dom}(u) \wedge u(x) \in \text{dom}(v)

Let E,FE, F, and GG be vector spaces over a ring RR. For partial linear maps u:EFu: E \to F and v:FGv: F \to G, an element xEx \in E is in the domain of the restricted composition vruv \circ_r u if and only if there exists ydom(u)y \in \text{dom}(u) such that x=yx = y and there exists ydom(v)y' \in \text{dom}(v) such that u(y)=yu(y) = y'.

theorem

xdom(vru)    u(x)dom(v)x \in \text{dom}(v \circ_r u) \implies u(x) \in \text{dom}(v)

For partial linear maps u:EFu: E \to F and v:FGv: F \to G, if xx is an element of the domain of the restricted composition vruv \circ_r u, then its image u(x)u(x) is contained in the domain of vv.

theorem

(vru)(x)=v(u(x))(v \circ_r u)(x) = v(u(x)) for partial linear maps

Let u:EFu: E \to F and v:FGv: F \to G be partial linear maps between modules over a ring RR. For any element xx in the domain of the restricted composition vruv \circ_r u, the value of the composition is given by (vru)(x)=v(u(x))(v \circ_r u)(x) = v(u(x)).

theorem

gr0=0g \circ_r 0 = 0 for partial linear maps

For any partial linear map g:FGg: F \to G between modules FF and GG over a ring RR, and for the zero partial linear map 0:EF0: E \to F (whose domain is the entire module EE), their restricted composition satisfies gr0=0g \circ_r 0 = 0. Here, 00 on the right-hand side denotes the zero partial linear map from EE to GG.

theorem

(f1rf2)rf3=f1r(f2rf3)(f_1 \circ_r f_2) \circ_r f_3 = f_1 \circ_r (f_2 \circ_r f_3) for partial linear maps

Let E,F,G,E, F, G, and HH be modules over a ring RR. For any partial linear maps f1:GHf_1 : G \to H, f2:FGf_2 : F \to G, and f3:EFf_3 : E \to F, the restricted composition r\circ_r is associative, meaning (f1rf2)rf3=f1r(f2rf3)(f_1 \circ_r f_2) \circ_r f_3 = f_1 \circ_r (f_2 \circ_r f_3).

theorem

vru=vuv \circ_r u = v \circ u when the range of uu is contained in the domain of vv

Let E,FE, F, and GG be modules over a ring RR. Let u:EFu: E \to F and v:FGv: F \to G be partial linear maps. If for every xx in the domain of uu, the image u(x)u(x) is contained in the domain of vv, then the restricted composition vruv \circ_r u is equal to the standard composition vuv \circ u (denoted as `v.comp u h`).

theorem

v(uS)vruv \circ (u|_S) \le v \circ_r u

Let E,F,E, F, and GG be modules over a ring RR. Let u:EFu: E \to F and v:FGv: F \to G be partial linear maps. For any submodule SS of EE, let uSu|_S denote the restriction of uu to the subdomain dom(u)S\text{dom}(u) \cap S. If the image of uSu|_S is contained in the domain of vv (i.e., xdom(uS),u(x)dom(v)\forall x \in \text{dom}(u|_S), u(x) \in \text{dom}(v)), then the composition v(uS)v \circ (u|_S) is less than or equal to the restricted composition vruv \circ_r u. Here, fgf \le g means that dom(f)dom(g)\text{dom}(f) \subseteq \text{dom}(g) and f(x)=g(x)f(x) = g(x) for all xdom(f)x \in \text{dom}(f), and the restricted composition vruv \circ_r u is the partial linear map with domain {xdom(u)u(x)dom(v)}\{x \in \text{dom}(u) \mid u(x) \in \text{dom}(v)\}.

theorem

Left Monotonicity of Restricted Composition: gg    grfgrfg \le g' \implies g \circ_r f \le g' \circ_r f

Let E,F,E, F, and GG be modules over a ring RR. Let f:EFf: E \to F be a partial linear map, and let g,g:FGg, g': F \to G be partial linear maps. If ggg \le g', then the restricted compositions satisfy grfgrfg \circ_r f \le g' \circ_r f. Here, ggg \le g' denotes that the domain of gg is a submodule of the domain of gg' and g(x)=g(x)g(x) = g'(x) for all xdom(g)x \in \text{dom}(g), and r\circ_r denotes the restricted composition.

theorem

Right Monotonicity of Restricted Composition: ff    grfgrff \le f' \implies g \circ_r f \le g \circ_r f'

Let E,F,E, F, and GG be modules over a ring RR. Let g:FGg: F \to G be a partial linear map, and let f,f:EFf, f': E \to F be partial linear maps. If fff \le f', then the restricted compositions satisfy grfgrfg \circ_r f \le g \circ_r f'. Here, the relation fff \le f' means that the domain of ff is a submodule of the domain of ff' and f(x)=f(x)f(x) = f'(x) for all xdom(f)x \in \text{dom}(f), and r\circ_r denotes the restricted composition.

theorem

(g)rf=(grf)(-g) \circ_r f = -(g \circ_r f)

Given partial linear maps f:EFf: E \to F and g:FGg: F \to G, the restricted composition of the negation of gg with ff is equal to the negation of the restricted composition of gg with ff, which is expressed as (g)rf=(grf)(-g) \circ_r f = -(g \circ_r f).

theorem

gr(f)=(grf)g \circ_r (-f) = -(g \circ_r f)

Let f:EFf: E \to F and g:FGg: F \to G be partial linear maps between modules over a ring RR. The restricted composition of gg with the negation of ff is equal to the negation of the restricted composition of gg and ff, that is, gr(f)=(grf)g \circ_r (-f) = -(g \circ_r f).

theorem

(g1+g2)rf=g1rf+g2rf(g_1 + g_2) \circ_r f = g_1 \circ_r f + g_2 \circ_r f

For partial linear maps f:EFf: E \to F and g1,g2:FGg_1, g_2: F \to G, the restricted composition of the sum g1+g2g_1 + g_2 with ff is equal to the sum of the restricted compositions of g1g_1 and g2g_2 with ff: (g1+g2)rf=g1rf+g2rf(g_1 + g_2) \circ_r f = g_1 \circ_r f + g_2 \circ_r f where the restricted composition grfg \circ_r f is the partial linear map with domain {xdom(f)f(x)dom(g)}\{x \in \text{dom}(f) \mid f(x) \in \text{dom}(g)\}, and the sum of two partial linear maps has a domain equal to the intersection of their respective domains.

theorem

(g1g2)rf=g1rfg2rf(g_1 - g_2) \circ_r f = g_1 \circ_r f - g_2 \circ_r f

For partial linear maps f:EFf: E \to F and g1,g2:FGg_1, g_2: F \to G, the restricted composition of the difference g1g2g_1 - g_2 with ff is equal to the difference of the restricted compositions: (g1g2)rf=g1rfg2rf(g_1 - g_2) \circ_r f = g_1 \circ_r f - g_2 \circ_r f where the restricted composition grfg \circ_r f is the partial linear map whose domain is {xdom(f)f(x)dom(g)}\{x \in \text{dom}(f) \mid f(x) \in \text{dom}(g)\}.

theorem

grf1+grf2gr(f1+f2)g \circ_r f_1 + g \circ_r f_2 \leq g \circ_r (f_1 + f_2) for partial linear maps

For any partial linear maps f1,f2f_1, f_2 from EE to FF and gg from FF to GG, the sum of the restricted compositions grf1g \circ_r f_1 and grf2g \circ_r f_2 is less than or equal to the restricted composition of gg with the sum f1+f2f_1 + f_2: grf1+grf2gr(f1+f2)g \circ_r f_1 + g \circ_r f_2 \leq g \circ_r (f_1 + f_2) In the context of partial linear maps, the inequality LML \leq M means that the domain of LL is a subset of the domain of MM, and the maps agree on the domain of LL.

theorem

grf1grf2gr(f1f2)g \circ_r f_1 - g \circ_r f_2 \le g \circ_r (f_1 - f_2) for partial linear maps

For any partial linear maps f1,f2f_1, f_2 from EE to FF and gg from FF to GG, the difference of the restricted compositions of gg with f1f_1 and f2f_2 is less than or equal to the restricted composition of gg with the difference f1f2f_1 - f_2: grf1grf2gr(f1f2)g \circ_r f_1 - g \circ_r f_2 \le g \circ_r (f_1 - f_2) where the inequality ABA \le B between partial linear maps signifies that AA is a restriction of BB (i.e., dom(A)dom(B)\text{dom}(A) \subseteq \text{dom}(B) and A(x)=B(x)A(x) = B(x) for all xdom(A)x \in \text{dom}(A)).

theorem

gr(cf)=c(grf)g \circ_r (c \cdot f) = c \cdot (g \circ_r f) for non-zero cc

Let SS be a division ring and E,F,GE, F, G be modules over SS. Given partial linear maps f:EFf: E \to F and g:FGg: F \to G, and a non-zero scalar cSc \in S, the restricted composition of gg with the scalar multiple cfc \cdot f is equal to the scalar multiple of the restricted composition of gg with ff. That is, gr(cf)=c(grf),g \circ_r (c \cdot f) = c \cdot (g \circ_r f), where the restricted composition hrkh \circ_r k of two partial linear maps is defined on the domain {xdom(k)k(x)dom(h)}\{x \in \text{dom}(k) \mid k(x) \in \text{dom}(h)\}.

theorem

(cg)rf=c(grf)(c \cdot g) \circ_r f = c \cdot (g \circ_r f) for partial linear maps

Let MM be a monoid and E,F,GE, F, G be modules over a ring RR. Suppose MM has a distributive action on GG that commutes with the action of RR. For any scalar cMc \in M and any partial linear maps f:EFf: E \to F and g:FGg: F \to G, the restricted composition of cgc \cdot g with ff is equal to the scalar multiple of the restricted composition of gg with ff: (cg)rf=c(grf),(c \cdot g) \circ_r f = c \cdot (g \circ_r f), where the restricted composition hrkh \circ_r k is defined on the domain {xdom(k)k(x)dom(h)}\{x \in \text{dom}(k) \mid k(x) \in \text{dom}(h)\}.

instance

Monoid of partial linear maps EEE \to E under restricted composition

Let EE be a module over a ring RR. The set of partial linear maps from EE to itself forms a monoid. The multiplication operation is the restricted composition grfg \circ_r f, whose domain is {xdom(f)f(x)dom(g)}\{x \in \text{dom}(f) \mid f(x) \in \text{dom}(g)\}, and the identity element is the identity linear map idE\text{id}_E defined on the entire space EE.

theorem

f1f2=f1rf2f_1 * f_2 = f_1 \circ_r f_2 for partial linear maps

For any two partial linear maps f1,f2f_1, f_2 from a module EE to itself, their product f1f2f_1 * f_2 in the monoid of partial linear maps is equal to their restricted composition f1rf2f_1 \circ_r f_2. The restricted composition is defined on the domain {xdom(f2)f2(x)dom(f1)}\{x \in \text{dom}(f_2) \mid f_2(x) \in \text{dom}(f_1)\}.

theorem

The domain of the identity partial linear map is \top

Let EE be a module over a ring RR. In the monoid of partial linear maps from EE to itself, the domain of the identity element 11 is the entire module EE, denoted by \top.

theorem

The underlying linear map of the identity partial linear map 11 is the canonical map from \top to EE.

Let EE be a module over a ring RR. The identity element 11 in the monoid of partial linear maps from EE to itself (under restricted composition) is defined such that its underlying linear map is equal to the canonical linear map from the universal submodule \top of EE to EE.

theorem

The underlying function of the identity partial linear map 11 is the identity map on EE

Let EE be a module over a ring RR. The function underlying the identity element 11 in the monoid of partial linear maps from EE to itself is equal to the function of the linear map identifying the top submodule \top (the entire space EE) with EE.

theorem

ker(f1)={0}\ker(f^{-1}) = \{0\}

For any partial linear map ff, the kernel of its inverse partial linear map f1f^{-1} is the trivial subspace {0}\{0\}.

theorem

The inverse of the inverse of a partial linear map ff is ff

For any partial linear map ff, the inverse of the inverse of ff is equal to ff. A partial linear map is defined as a linear map whose domain is a submodule of the total space.

theorem

f1rff^{-1} \circ_r f equals the identity map on the domain of ff

Let ff be a partial linear map with domain dom(f)\text{dom}(f). The restricted composition of the inverse of ff and ff, denoted f1rff^{-1} \circ_r f, is equal to the identity map restricted to dom(f)\text{dom}(f).

theorem

frf1f \circ_r f^{-1} equals the identity on the domain of f1f^{-1}

For any partial linear map ff, the restricted composition of ff with its inverse f1f^{-1} (denoted frf1f \circ_r f^{-1}) is equal to the identity map restricted to the domain of f1f^{-1}. That is, frf1=iddom(f1)f \circ_r f^{-1} = \text{id}_{\text{dom}(f^{-1})}.