Physlib

PhyslibAlpha.AlgebraicFramework.JordanOrderUnit.FreeSpecialTwo

The free special Jordan algebra on two generators

Let `A₂ = FreeAlgebra ℝ (Fin 2)`. Mathlib's `SymAlg A₂` is its normalized Jordanization, with product `x ∘ y = (xy + yx)/2`. The free special Jordan algebra on two generators is the Jordan fragment of that symmetrization generated by the two canonical free-associative letters.

This is only the concrete special side of Shirshov--Cohn. It deliberately does not claim that the abstract free Jordan algebra maps injectively here (Shirshov), nor that every quotient remains special (Cohn); those are the two distinct hard theorems to be formalized above this object.

16 declarations

abbrev

Free associative real algebra on two generators

The free associative algebra over the real numbers R\mathbb{R} generated by two elements. This corresponds to the algebra of polynomials in two non-commuting variables with real coefficients.

instance

22 is invertible in the free associative real algebra on two generators

In the free associative real algebra on two generators, the natural number 22 is an invertible element. This is established by mapping the inverse of the real number 22 into the algebra via the canonical algebra map R→FreeAssocTwo\mathbb{R} \to \text{FreeAssocTwo}.

instance

Non-associative commutative ring structure on SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo})

The algebra SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}), which is the symmetrization of the free associative algebra over R\mathbb{R} on two generators, is equipped with the structure of a non-associative commutative ring. The addition is inherited from the underlying associative algebra, and the multiplication is the symmetrized Jordan product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx).

instance

Scalar multiplication on SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo})

This definition provides a scalar multiplication of the Jordan algebra SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) on itself. For any two elements x,y∈SymAlg(FreeAssocTwo)x, y \in \text{SymAlg}(\text{FreeAssocTwo}), the scalar multiplication x⋅yx \cdot y is defined as their product in the algebra, which is the symmetrized Jordan product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx) derived from the underlying free associative algebra FreeAssocTwo\text{FreeAssocTwo}.

instance

Scalar Tower Property for SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) over R\mathbb{R}

Let J=SymAlg(FreeAssocTwo)J = \text{SymAlg}(\text{FreeAssocTwo}) be the Jordanization of the free associative algebra over R\mathbb{R} on two generators, where the Jordan product is defined as x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx). For any scalar r∈Rr \in \mathbb{R} and elements x,y∈Jx, y \in J, the scalar tower property (r⋅x)∘y=r⋅(x∘y)(r \cdot x) \circ y = r \cdot (x \circ y) holds.

instance

(r⋅x)∘y=x∘(r⋅y)(r \cdot x) \circ y = x \circ (r \cdot y) in SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo})

In the Jordanization of the free associative real algebra on two generators, denoted by SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}), scalar multiplication by real numbers commutes with the Jordan product. Specifically, for any scalar r∈Rr \in \mathbb{R} and any elements x,y∈SymAlg(FreeAssocTwo)x, y \in \text{SymAlg}(\text{FreeAssocTwo}), the following equality holds: (r⋅x)∘y=x∘(r⋅y)(r \cdot x) \circ y = x \circ (r \cdot y) where ∘\circ denotes the symmetrized Jordan product defined as x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx).

definition

First generator XX of the free special Jordan algebra

The element representing the first canonical generator XX in the Jordanization of the free associative real algebra on two generators. The Jordanization, denoted SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}), is the algebra equipped with the symmetrized Jordan product a∘b=12(ab+ba)a \circ b = \frac{1}{2}(ab + ba), and this definition identifies the first generator (index 0) of the underlying free associative algebra as an element of this Jordan algebra.

definition

Second generator YY of the free special Jordan algebra

The element in the Jordanization of the free associative real algebra on two generators that corresponds to the second canonical generator YY. The Jordanization SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) is the algebra equipped with the symmetrized Jordan product a∘b=12(ab+ba)a \circ b = \frac{1}{2}(ab + ba).

abbrev

Submodule of the free special Jordan algebra on two generators

The R\mathbb{R}-submodule of the Jordanization SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) generated by the two canonical elements XX and YY. Here, SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) is the free associative algebra over R\mathbb{R} on two generators equipped with the symmetrized Jordan product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx). This submodule constitutes the carrier set of the free special Jordan algebra on two generators.

abbrev

Free special Jordan algebra on two generators

The type representing the free special Jordan algebra on two generators. It is defined as the unital real Jordan subalgebra of SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) generated by the two canonical elements XX and YY. Here, SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) denotes the Jordanization of the free associative algebra over R\mathbb{R} on two generators, equipped with the symmetrized Jordan product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx).

theorem

X∈freeSpecialJordanTwoX \in \text{freeSpecialJordanTwo}

Let FreeAssocTwo\text{FreeAssocTwo} be the free associative algebra over R\mathbb{R} on two generators, and let SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) be its Jordanization with the symmetrized product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx). If XX is the first canonical generator (denoted `freeSpecialX`) and freeSpecialJordanTwo\text{freeSpecialJordanTwo} is the R\mathbb{R}-submodule of SymAlg(FreeAssocTwo)\text{SymAlg}(\text{FreeAssocTwo}) generated by the two canonical generators, then X∈freeSpecialJordanTwoX \in \text{freeSpecialJordanTwo}.

theorem

The second generator YY belongs to the free special Jordan algebra on two generators

Let YY be the second canonical generator of the free associative algebra over R\mathbb{R} on two generators. Let the free special Jordan algebra on two generators be the R\mathbb{R}-submodule of the Jordanization (equipped with the symmetrized product x∘y=12(xy+yx)x \circ y = \frac{1}{2}(xy + yx)) generated by the two canonical elements XX and YY. Then YY is an element of this free special Jordan algebra.

definition

Canonical generators of FreeSpecialJordanTwo\text{FreeSpecialJordanTwo}

This function maps the two indices of {0,1}\{0, 1\} to the two canonical generators of the free special Jordan algebra on two generators. Specifically, index 00 is mapped to the first generator XX and index 11 is mapped to the second generator YY, both regarded as elements of the subalgebra FreeSpecialJordanTwo⊆SymAlg(FreeAssocTwo)\text{FreeSpecialJordanTwo} \subseteq \text{SymAlg}(\text{FreeAssocTwo}).

definition

Canonical homomorphism FreeJordanTwo→FreeSpecialJordanTwo\text{FreeJordanTwo} \to \text{FreeSpecialJordanTwo}

The canonical unital Jordan homomorphism from the free unital real Jordan algebra on two generators, FreeJordanTwo\text{FreeJordanTwo}, to the free special Jordan algebra on two generators, FreeSpecialJordanTwo\text{FreeSpecialJordanTwo}. This map is defined using the universal property of the free Jordan algebra by sending its two abstract generators to the canonical generators XX and YY of the special Jordan algebra. Shirshov's theorem states that this homomorphism is injective.

theorem

The image of the first generator xx under the canonical homomorphism freeJordanToSpecial\text{freeJordanToSpecial} is XX

Let FreeJordanTwo\text{FreeJordanTwo} be the free unital real Jordan algebra on two generators and FreeSpecialJordanTwo\text{FreeSpecialJordanTwo} be the free special Jordan algebra on two generators. Let ϕ:FreeJordanTwo→FreeSpecialJordanTwo\phi: \text{FreeJordanTwo} \to \text{FreeSpecialJordanTwo} be the canonical unital Jordan homomorphism. Let xx be the first abstract generator of FreeJordanTwo\text{FreeJordanTwo} and XX be the first canonical generator of FreeSpecialJordanTwo\text{FreeSpecialJordanTwo} (associated with index 0). Then ϕ(x)=X\phi(x) = X.

theorem

The canonical map FreeJordanTwo→FreeSpecialJordanTwo\text{FreeJordanTwo} \to \text{FreeSpecialJordanTwo} sends the second generator yy to YY

Let FreeJordanTwo\text{FreeJordanTwo} be the free unital real Jordan algebra on two generators and FreeSpecialJordanTwo\text{FreeSpecialJordanTwo} be the free special Jordan algebra on two generators. Let ϕ:FreeJordanTwo→FreeSpecialJordanTwo\phi: \text{FreeJordanTwo} \to \text{FreeSpecialJordanTwo} be the canonical unital Jordan homomorphism. If y∈FreeJordanTwoy \in \text{FreeJordanTwo} is the second abstract generator and Y∈FreeSpecialJordanTwoY \in \text{FreeSpecialJordanTwo} is the second canonical generator (indexed by 11), then ϕ(y)=Y\phi(y) = Y.