Metamath Proof Explorer


Theorem readdid1addid2d

Description: Given some real number B where A acts like a right additive identity, derive that A is a left additive identity. Note that the hypothesis is weaker than proving that A is a right additive identity (for all numbers). Although, if there is a right additive identity, then by readdcan , A is the right additive identity. (Contributed by Steven Nguyen, 14-Jan-2023)

Ref Expression
Hypotheses readdid1addid2d.a ( 𝜑𝐴 ∈ ℝ )
readdid1addid2d.b ( 𝜑𝐵 ∈ ℝ )
readdid1addid2d.1 ( 𝜑 → ( 𝐵 + 𝐴 ) = 𝐵 )
Assertion readdid1addid2d ( ( 𝜑𝐶 ∈ ℝ ) → ( 𝐴 + 𝐶 ) = 𝐶 )

Proof

Step Hyp Ref Expression
1 readdid1addid2d.a ( 𝜑𝐴 ∈ ℝ )
2 readdid1addid2d.b ( 𝜑𝐵 ∈ ℝ )
3 readdid1addid2d.1 ( 𝜑 → ( 𝐵 + 𝐴 ) = 𝐵 )
4 2 adantr ( ( 𝜑𝐶 ∈ ℝ ) → 𝐵 ∈ ℝ )
5 4 recnd ( ( 𝜑𝐶 ∈ ℝ ) → 𝐵 ∈ ℂ )
6 1 adantr ( ( 𝜑𝐶 ∈ ℝ ) → 𝐴 ∈ ℝ )
7 6 recnd ( ( 𝜑𝐶 ∈ ℝ ) → 𝐴 ∈ ℂ )
8 simpr ( ( 𝜑𝐶 ∈ ℝ ) → 𝐶 ∈ ℝ )
9 8 recnd ( ( 𝜑𝐶 ∈ ℝ ) → 𝐶 ∈ ℂ )
10 5 7 9 addassd ( ( 𝜑𝐶 ∈ ℝ ) → ( ( 𝐵 + 𝐴 ) + 𝐶 ) = ( 𝐵 + ( 𝐴 + 𝐶 ) ) )
11 3 adantr ( ( 𝜑𝐶 ∈ ℝ ) → ( 𝐵 + 𝐴 ) = 𝐵 )
12 11 oveq1d ( ( 𝜑𝐶 ∈ ℝ ) → ( ( 𝐵 + 𝐴 ) + 𝐶 ) = ( 𝐵 + 𝐶 ) )
13 10 12 eqtr3d ( ( 𝜑𝐶 ∈ ℝ ) → ( 𝐵 + ( 𝐴 + 𝐶 ) ) = ( 𝐵 + 𝐶 ) )
14 6 8 readdcld ( ( 𝜑𝐶 ∈ ℝ ) → ( 𝐴 + 𝐶 ) ∈ ℝ )
15 readdcan ( ( ( 𝐴 + 𝐶 ) ∈ ℝ ∧ 𝐶 ∈ ℝ ∧ 𝐵 ∈ ℝ ) → ( ( 𝐵 + ( 𝐴 + 𝐶 ) ) = ( 𝐵 + 𝐶 ) ↔ ( 𝐴 + 𝐶 ) = 𝐶 ) )
16 14 8 4 15 syl3anc ( ( 𝜑𝐶 ∈ ℝ ) → ( ( 𝐵 + ( 𝐴 + 𝐶 ) ) = ( 𝐵 + 𝐶 ) ↔ ( 𝐴 + 𝐶 ) = 𝐶 ) )
17 13 16 mpbid ( ( 𝜑𝐶 ∈ ℝ ) → ( 𝐴 + 𝐶 ) = 𝐶 )