Metamath Proof Explorer


Definition df-finfld

Description: Define a function taking a prime power q to the finite field of order q . When q is an integer, there is a field of order q (that is, its base set has q elements) if and only if q is a prime power. Additionally, any two finite fields of the same order are isomorphic. Thus, we usually refer to "the" finite field of order q — which is often denoted 𝔽 q — without specifying a particular one. Usually, this causes no problems, but in Metamath the notation ( finFldq ) must unambigously denote a specific set. Since HFStructs can be well-ordered, we can use the smallest candidate according to the ordering. This depends on the fact that any finite field is isomorphic to an HFStruct. Indeed, this isomorphism result holds for most abstract mathematical structures with a finite base set. (For groups, see fingrphf .) Thus, the technique used here could apply in other cases in which we want a particular representative of some class of finite structures. (Contributed by Eric Schmidt, 24-Oct-2026)

Ref Expression
Assertion df-finfld 𝔽 = ( 𝑞 ∈ ( ↑ “ ( ℙ × ℕ ) ) ↦ inf ( ( HFStruct ∩ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 } ) , HFStruct , <HFStruct ) )

Detailed syntax breakdown

Step Hyp Ref Expression
0 cfinfld ⊢ 𝔽
1 vq ⊢ 𝑞
2 cexp ⊢ ↑
3 cprime ⊢ ℙ
4 cn ⊢ ℕ
5 3 4 cxp ⊢ ( ℙ × ℕ )
6 2 5 cima ⊢ ( ↑ “ ( ℙ × ℕ ) )
7 chfstruct ⊢ HFStruct
8 vk ⊢ 𝑘
9 cfield ⊢ Field
10 chash ⊢ ♯
11 cbs ⊢ Base
12 8 cv ⊢ 𝑘
13 12 11 cfv ⊢ ( Base ‘ 𝑘 )
14 13 10 cfv ⊢ ( ♯ ‘ ( Base ‘ 𝑘 ) )
15 1 cv ⊢ 𝑞
16 14 15 wceq ⊢ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞
17 16 8 9 crab ⊢ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 }
18 7 17 cin ⊢ ( HFStruct ∩ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 } )
19 clthfstruct ⊢ <HFStruct
20 18 7 19 cinf ⊢ inf ( ( HFStruct ∩ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 } ) , HFStruct , <HFStruct )
21 1 6 20 cmpt ⊢ ( 𝑞 ∈ ( ↑ “ ( ℙ × ℕ ) ) ↦ inf ( ( HFStruct ∩ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 } ) , HFStruct , <HFStruct ) )
22 0 21 wceq ⊢ 𝔽 = ( 𝑞 ∈ ( ↑ “ ( ℙ × ℕ ) ) ↦ inf ( ( HFStruct ∩ { 𝑘 ∈ Field ∣ ( ♯ ‘ ( Base ‘ 𝑘 ) ) = 𝑞 } ) , HFStruct , <HFStruct ) )