| Step | Hyp | Ref | Expression | 
|---|
| 1 |  | sbcex 3797 | . 2
⊢
([𝐴 / 𝑥]𝐵𝑅𝐶 → 𝐴 ∈ V) | 
| 2 |  | br0 5191 | . . . 4
⊢  ¬
⦋𝐴 / 𝑥⦌𝐵∅⦋𝐴 / 𝑥⦌𝐶 | 
| 3 |  | csbprc 4408 | . . . . 5
⊢ (¬
𝐴 ∈ V →
⦋𝐴 / 𝑥⦌𝑅 = ∅) | 
| 4 | 3 | breqd 5153 | . . . 4
⊢ (¬
𝐴 ∈ V →
(⦋𝐴 / 𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶 ↔ ⦋𝐴 / 𝑥⦌𝐵∅⦋𝐴 / 𝑥⦌𝐶)) | 
| 5 | 2, 4 | mtbiri 327 | . . 3
⊢ (¬
𝐴 ∈ V → ¬
⦋𝐴 / 𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶) | 
| 6 | 5 | con4i 114 | . 2
⊢
(⦋𝐴 /
𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶 → 𝐴 ∈ V) | 
| 7 |  | dfsbcq2 3790 | . . 3
⊢ (𝑦 = 𝐴 → ([𝑦 / 𝑥]𝐵𝑅𝐶 ↔ [𝐴 / 𝑥]𝐵𝑅𝐶)) | 
| 8 |  | csbeq1 3901 | . . . 4
⊢ (𝑦 = 𝐴 → ⦋𝑦 / 𝑥⦌𝐵 = ⦋𝐴 / 𝑥⦌𝐵) | 
| 9 |  | csbeq1 3901 | . . . 4
⊢ (𝑦 = 𝐴 → ⦋𝑦 / 𝑥⦌𝑅 = ⦋𝐴 / 𝑥⦌𝑅) | 
| 10 |  | csbeq1 3901 | . . . 4
⊢ (𝑦 = 𝐴 → ⦋𝑦 / 𝑥⦌𝐶 = ⦋𝐴 / 𝑥⦌𝐶) | 
| 11 | 8, 9, 10 | breq123d 5156 | . . 3
⊢ (𝑦 = 𝐴 → (⦋𝑦 / 𝑥⦌𝐵⦋𝑦 / 𝑥⦌𝑅⦋𝑦 / 𝑥⦌𝐶 ↔ ⦋𝐴 / 𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶)) | 
| 12 |  | nfcsb1v 3922 | . . . . 5
⊢
Ⅎ𝑥⦋𝑦 / 𝑥⦌𝐵 | 
| 13 |  | nfcsb1v 3922 | . . . . 5
⊢
Ⅎ𝑥⦋𝑦 / 𝑥⦌𝑅 | 
| 14 |  | nfcsb1v 3922 | . . . . 5
⊢
Ⅎ𝑥⦋𝑦 / 𝑥⦌𝐶 | 
| 15 | 12, 13, 14 | nfbr 5189 | . . . 4
⊢
Ⅎ𝑥⦋𝑦 / 𝑥⦌𝐵⦋𝑦 / 𝑥⦌𝑅⦋𝑦 / 𝑥⦌𝐶 | 
| 16 |  | csbeq1a 3912 | . . . . 5
⊢ (𝑥 = 𝑦 → 𝐵 = ⦋𝑦 / 𝑥⦌𝐵) | 
| 17 |  | csbeq1a 3912 | . . . . 5
⊢ (𝑥 = 𝑦 → 𝑅 = ⦋𝑦 / 𝑥⦌𝑅) | 
| 18 |  | csbeq1a 3912 | . . . . 5
⊢ (𝑥 = 𝑦 → 𝐶 = ⦋𝑦 / 𝑥⦌𝐶) | 
| 19 | 16, 17, 18 | breq123d 5156 | . . . 4
⊢ (𝑥 = 𝑦 → (𝐵𝑅𝐶 ↔ ⦋𝑦 / 𝑥⦌𝐵⦋𝑦 / 𝑥⦌𝑅⦋𝑦 / 𝑥⦌𝐶)) | 
| 20 | 15, 19 | sbiev 2313 | . . 3
⊢ ([𝑦 / 𝑥]𝐵𝑅𝐶 ↔ ⦋𝑦 / 𝑥⦌𝐵⦋𝑦 / 𝑥⦌𝑅⦋𝑦 / 𝑥⦌𝐶) | 
| 21 | 7, 11, 20 | vtoclbg 3556 | . 2
⊢ (𝐴 ∈ V → ([𝐴 / 𝑥]𝐵𝑅𝐶 ↔ ⦋𝐴 / 𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶)) | 
| 22 | 1, 6, 21 | pm5.21nii 378 | 1
⊢
([𝐴 / 𝑥]𝐵𝑅𝐶 ↔ ⦋𝐴 / 𝑥⦌𝐵⦋𝐴 / 𝑥⦌𝑅⦋𝐴 / 𝑥⦌𝐶) |