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Description: The base set of a commutative monoid is its center. (Contributed by SN, 21-Mar-2025)
| Ref | Expression | ||
|---|---|---|---|
| Hypotheses | cmnbascntr.b | ⊢ 𝐵 = ( Base ‘ 𝐺 ) | |
| cmnbascntr.z | ⊢ 𝑍 = ( Cntr ‘ 𝐺 ) | ||
| Assertion | cmnbascntr | ⊢ ( 𝐺 ∈ CMnd → 𝐵 = 𝑍 ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | cmnbascntr.b | ⊢ 𝐵 = ( Base ‘ 𝐺 ) | |
| 2 | cmnbascntr.z | ⊢ 𝑍 = ( Cntr ‘ 𝐺 ) | |
| 3 | eqid | ⊢ ( Cntz ‘ 𝐺 ) = ( Cntz ‘ 𝐺 ) | |
| 4 | 1 3 | cntrval | ⊢ ( ( Cntz ‘ 𝐺 ) ‘ 𝐵 ) = ( Cntr ‘ 𝐺 ) |
| 5 | ssid | ⊢ 𝐵 ⊆ 𝐵 | |
| 6 | eqid | ⊢ ( +g ‘ 𝐺 ) = ( +g ‘ 𝐺 ) | |
| 7 | 1 6 3 | cntzval | ⊢ ( 𝐵 ⊆ 𝐵 → ( ( Cntz ‘ 𝐺 ) ‘ 𝐵 ) = { 𝑥 ∈ 𝐵 ∣ ∀ 𝑦 ∈ 𝐵 ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) } ) |
| 8 | 5 7 | ax-mp | ⊢ ( ( Cntz ‘ 𝐺 ) ‘ 𝐵 ) = { 𝑥 ∈ 𝐵 ∣ ∀ 𝑦 ∈ 𝐵 ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) } |
| 9 | 2 4 8 | 3eqtr2i | ⊢ 𝑍 = { 𝑥 ∈ 𝐵 ∣ ∀ 𝑦 ∈ 𝐵 ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) } |
| 10 | 1 6 | cmncom | ⊢ ( ( 𝐺 ∈ CMnd ∧ 𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ) → ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) ) |
| 11 | 10 | 3expa | ⊢ ( ( ( 𝐺 ∈ CMnd ∧ 𝑥 ∈ 𝐵 ) ∧ 𝑦 ∈ 𝐵 ) → ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) ) |
| 12 | 11 | ralrimiva | ⊢ ( ( 𝐺 ∈ CMnd ∧ 𝑥 ∈ 𝐵 ) → ∀ 𝑦 ∈ 𝐵 ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) ) |
| 13 | 12 | rabeqcda | ⊢ ( 𝐺 ∈ CMnd → { 𝑥 ∈ 𝐵 ∣ ∀ 𝑦 ∈ 𝐵 ( 𝑥 ( +g ‘ 𝐺 ) 𝑦 ) = ( 𝑦 ( +g ‘ 𝐺 ) 𝑥 ) } = 𝐵 ) |
| 14 | 9 13 | eqtr2id | ⊢ ( 𝐺 ∈ CMnd → 𝐵 = 𝑍 ) |