# mathlibdocumentation

ring_theory.derivation

# Derivations

This file defines derivation. A derivation D from the R-algebra A to the A-module M is an R-linear map that satisfy the Leibniz rule D (a * b) = a * D b + D a * b.

## Notation

The notation ⁅D1, D2⁆ is used for the commutator of two derivations.

TODO: this file is just a stub to go on with some PRs in the geometry section. It only implements the definition of derivations in commutative algebra. This will soon change: as soon as bimodules will be there in mathlib I will change this file to take into account the non-commutative case. Any development on the theory of derivations is discouraged until the definitive definition of derivation will be implemented.

structure derivation (R : Type u_1) (A : Type u_2) [ A] (M : Type u_3) [ M] [ M] [ M] :
Type (max u_2 u_3)

D : derivation R A M is an R-linear map from A to M that satisfies the leibniz equality. TODO: update this when bimodules are defined.

@[instance]
def derivation.has_coe_to_fun {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :

Equations
@[instance]
def derivation.has_coe_to_linear_map {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :
has_coe A M) (A →ₗ[R] M)

Equations
@[simp]
theorem derivation.to_fun_eq_coe {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) :

@[simp]
theorem derivation.coe_fn_coe {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (f : A M) :

theorem derivation.coe_injective {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] {D1 D2 : A M} :
D1 = D2D1 = D2

@[ext]
theorem derivation.ext {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] {D1 D2 : A M} :
(∀ (a : A), D1 a = D2 a)D1 = D2

@[simp]
theorem derivation.map_add {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (a b : A) :
D (a + b) = D a + D b

@[simp]
theorem derivation.map_zero {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) :
D 0 = 0

@[simp]
theorem derivation.map_smul {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (r : R) (a : A) :
D (r a) = r D a

@[simp]
theorem derivation.leibniz {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (a b : A) :
D (a * b) = a D b + b D a

@[simp]
theorem derivation.map_one_eq_zero {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) :
D 1 = 0

@[simp]
theorem derivation.map_algebra_map {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (r : R) :
D ( A) r) = 0

@[instance]
def derivation.has_zero {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :

Equations
@[instance]
def derivation.inhabited {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :

Equations
@[instance]
def derivation.add_comm_monoid {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :

Equations
@[simp]
theorem derivation.add_apply {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] {D1 D2 : A M} (a : A) :
(D1 + D2) a = D1 a + D2 a

@[instance]
def derivation.derivation.Rsemimodule {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :
A M)

Equations
@[simp]
theorem derivation.smul_to_linear_map_coe {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (r : R) :
(r D) = r D

@[simp]
theorem derivation.Rsmul_apply {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (r : R) (a : A) :
(r D) a = r D a

@[instance]
def derivation.semimodule {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :
A M)

Equations
@[simp]
theorem derivation.smul_apply {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (a b : A) :
(a D) b = a D b

@[instance]
def derivation.is_scalar_tower {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] [ M] :
A M)

@[simp]
theorem derivation.map_neg {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (a : A) :
D (-a) = -D a

@[simp]
theorem derivation.map_sub {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] {M : Type u_3} [ M] [ M] [ M] (D : A M) (a b : A) :
D (a - b) = D a - D b

@[instance]
def derivation.add_comm_group {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] {M : Type u_3} [ M] [ M] [ M] :

Equations

# Lie structures

def derivation.commutator {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] :
A A A A A A

The commutator of derivations is again a derivation.

Equations
@[instance]
def derivation.has_bracket {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] :

Equations
@[simp]
theorem derivation.commutator_coe_linear_map {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] {D1 D2 : A A} :

theorem derivation.commutator_apply {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] {D1 D2 : A A} (a : A) :
D1,D2 a = D1 (D2 a) - D2 (D1 a)

@[instance]
def derivation.lie_ring {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] :

Equations
@[instance]
def derivation.lie_algebra {R : Type u_1} [comm_ring R] {A : Type u_2} [comm_ring A] [ A] :
A A)

Equations
def linear_map.comp_der {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] {N : Type u_4} [ N] [ N] [ M] [ N] :
(M →ₗ[A] N) A M A N

The composition of a linear map and a derivation is a derivation.

Equations
@[simp]
theorem linear_map.comp_der_apply {R : Type u_1} {A : Type u_2} [ A] {M : Type u_3} [ M] [ M] {N : Type u_4} [ N] [ N] [ M] [ N] (f : M →ₗ[A] N) (D : A M) (a : A) :
(f.comp_der D) a = f (D a)