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Metamath Proof Explorer

Theorem dpjid

Description: The key property of projections: the sum of all the projections of A is A . (Contributed by Mario Carneiro, 26-Apr-2016)

Ref Expression
Hypotheses dpjfval.1 ⊢ ( 𝜑 → 𝐺 dom DProd 𝑆 )
dpjfval.2 ⊢ ( 𝜑 → dom 𝑆 = 𝐼 )
dpjfval.p ⊢ 𝑃 = ( 𝐺 dProj 𝑆 )
dpjid.3 ⊢ ( 𝜑 → 𝐴 ∈ ( 𝐺 DProd 𝑆 ) )
Assertion dpjid ( 𝜑 → 𝐴 = ( 𝐺 Σg ( 𝑥 ∈ 𝐼 ↦ ( ( 𝑃 ‘ 𝑥 ) ‘ 𝐴 ) ) ) )

Proof

Step Hyp Ref Expression
1 dpjfval.1 ⊢ ( 𝜑 → 𝐺 dom DProd 𝑆 )
2 dpjfval.2 ⊢ ( 𝜑 → dom 𝑆 = 𝐼 )
3 dpjfval.p ⊢ 𝑃 = ( 𝐺 dProj 𝑆 )
4 dpjid.3 ⊢ ( 𝜑 → 𝐴 ∈ ( 𝐺 DProd 𝑆 ) )
5 eqid ⊢ ( 0g ‘ 𝐺 ) = ( 0g ‘ 𝐺 )
6 eqid ⊢ { ℎ ∈ X 𝑖 ∈ 𝐼 ( 𝑆 ‘ 𝑖 ) ∣ ℎ finSupp ( 0g ‘ 𝐺 ) } = { ℎ ∈ X 𝑖 ∈ 𝐼 ( 𝑆 ‘ 𝑖 ) ∣ ℎ finSupp ( 0g ‘ 𝐺 ) }
7 1 2 3 4 5 6 dpjidcl ⊢ ( 𝜑 → ( ( 𝑥 ∈ 𝐼 ↦ ( ( 𝑃 ‘ 𝑥 ) ‘ 𝐴 ) ) ∈ { ℎ ∈ X 𝑖 ∈ 𝐼 ( 𝑆 ‘ 𝑖 ) ∣ ℎ finSupp ( 0g ‘ 𝐺 ) } ∧ 𝐴 = ( 𝐺 Σg ( 𝑥 ∈ 𝐼 ↦ ( ( 𝑃 ‘ 𝑥 ) ‘ 𝐴 ) ) ) ) )
8 7 simprd ⊢ ( 𝜑 → 𝐴 = ( 𝐺 Σg ( 𝑥 ∈ 𝐼 ↦ ( ( 𝑃 ‘ 𝑥 ) ‘ 𝐴 ) ) ) )