Detailed syntax breakdown of Definition df-se
| Step | Hyp | Ref
 | Expression | 
| 1 |   | cA | 
. . 3
class 𝐴 | 
| 2 |   | cR | 
. . 3
class 𝑅 | 
| 3 | 1, 2 | wse 4364 | 
. 2
wff 𝑅 Se 𝐴 | 
| 4 |   | vy | 
. . . . . . 7
setvar 𝑦 | 
| 5 | 4 | cv 1363 | 
. . . . . 6
class 𝑦 | 
| 6 |   | vx | 
. . . . . . 7
setvar 𝑥 | 
| 7 | 6 | cv 1363 | 
. . . . . 6
class 𝑥 | 
| 8 | 5, 7, 2 | wbr 4033 | 
. . . . 5
wff 𝑦𝑅𝑥 | 
| 9 | 8, 4, 1 | crab 2479 | 
. . . 4
class {𝑦 ∈ 𝐴 ∣ 𝑦𝑅𝑥} | 
| 10 |   | cvv 2763 | 
. . . 4
class
V | 
| 11 | 9, 10 | wcel 2167 | 
. . 3
wff {𝑦 ∈ 𝐴 ∣ 𝑦𝑅𝑥} ∈ V | 
| 12 | 11, 6, 1 | wral 2475 | 
. 2
wff
∀𝑥 ∈
𝐴 {𝑦 ∈ 𝐴 ∣ 𝑦𝑅𝑥} ∈ V | 
| 13 | 3, 12 | wb 105 | 
1
wff (𝑅 Se 𝐴 ↔ ∀𝑥 ∈ 𝐴 {𝑦 ∈ 𝐴 ∣ 𝑦𝑅𝑥} ∈ V) |