Metamath Proof Explorer


Theorem hoidmv0val

Description: The dimensional volume of a 0-dimensional half-open interval. Definition 115A (c) of Fremlin1 p. 29. (Contributed by Glauco Siliprandi, 21-Nov-2020)

Ref Expression
Hypotheses hoidmv0val.l 𝐿 = ( 𝑥 ∈ Fin ↦ ( 𝑎 ∈ ( ℝ ↑m 𝑥 ) , 𝑏 ∈ ( ℝ ↑m 𝑥 ) ↦ if ( 𝑥 = ∅ , 0 , ∏ 𝑘𝑥 ( vol ‘ ( ( 𝑎𝑘 ) [,) ( 𝑏𝑘 ) ) ) ) ) )
hoidmv0val.a ( 𝜑𝐴 : ∅ ⟶ ℝ )
hoidmv0val.b ( 𝜑𝐵 : ∅ ⟶ ℝ )
Assertion hoidmv0val ( 𝜑 → ( 𝐴 ( 𝐿 ‘ ∅ ) 𝐵 ) = 0 )

Proof

Step Hyp Ref Expression
1 hoidmv0val.l 𝐿 = ( 𝑥 ∈ Fin ↦ ( 𝑎 ∈ ( ℝ ↑m 𝑥 ) , 𝑏 ∈ ( ℝ ↑m 𝑥 ) ↦ if ( 𝑥 = ∅ , 0 , ∏ 𝑘𝑥 ( vol ‘ ( ( 𝑎𝑘 ) [,) ( 𝑏𝑘 ) ) ) ) ) )
2 hoidmv0val.a ( 𝜑𝐴 : ∅ ⟶ ℝ )
3 hoidmv0val.b ( 𝜑𝐵 : ∅ ⟶ ℝ )
4 0fin ∅ ∈ Fin
5 4 a1i ( 𝜑 → ∅ ∈ Fin )
6 1 2 3 5 hoidmvval ( 𝜑 → ( 𝐴 ( 𝐿 ‘ ∅ ) 𝐵 ) = if ( ∅ = ∅ , 0 , ∏ 𝑘 ∈ ∅ ( vol ‘ ( ( 𝐴𝑘 ) [,) ( 𝐵𝑘 ) ) ) ) )
7 eqid ∅ = ∅
8 iftrue ( ∅ = ∅ → if ( ∅ = ∅ , 0 , ∏ 𝑘 ∈ ∅ ( vol ‘ ( ( 𝐴𝑘 ) [,) ( 𝐵𝑘 ) ) ) ) = 0 )
9 7 8 ax-mp if ( ∅ = ∅ , 0 , ∏ 𝑘 ∈ ∅ ( vol ‘ ( ( 𝐴𝑘 ) [,) ( 𝐵𝑘 ) ) ) ) = 0
10 9 a1i ( 𝜑 → if ( ∅ = ∅ , 0 , ∏ 𝑘 ∈ ∅ ( vol ‘ ( ( 𝐴𝑘 ) [,) ( 𝐵𝑘 ) ) ) ) = 0 )
11 6 10 eqtrd ( 𝜑 → ( 𝐴 ( 𝐿 ‘ ∅ ) 𝐵 ) = 0 )