Detailed syntax breakdown of Definition df-cn
| Step | Hyp | Ref
 | Expression | 
| 1 |   | ccn 14421 | 
. 2
class 
Cn | 
| 2 |   | vj | 
. . 3
setvar 𝑗 | 
| 3 |   | vk | 
. . 3
setvar 𝑘 | 
| 4 |   | ctop 14233 | 
. . 3
class
Top | 
| 5 |   | vf | 
. . . . . . . . 9
setvar 𝑓 | 
| 6 | 5 | cv 1363 | 
. . . . . . . 8
class 𝑓 | 
| 7 | 6 | ccnv 4662 | 
. . . . . . 7
class ◡𝑓 | 
| 8 |   | vy | 
. . . . . . . 8
setvar 𝑦 | 
| 9 | 8 | cv 1363 | 
. . . . . . 7
class 𝑦 | 
| 10 | 7, 9 | cima 4666 | 
. . . . . 6
class (◡𝑓 “ 𝑦) | 
| 11 | 2 | cv 1363 | 
. . . . . 6
class 𝑗 | 
| 12 | 10, 11 | wcel 2167 | 
. . . . 5
wff (◡𝑓 “ 𝑦) ∈ 𝑗 | 
| 13 | 3 | cv 1363 | 
. . . . 5
class 𝑘 | 
| 14 | 12, 8, 13 | wral 2475 | 
. . . 4
wff
∀𝑦 ∈
𝑘 (◡𝑓 “ 𝑦) ∈ 𝑗 | 
| 15 | 13 | cuni 3839 | 
. . . . 5
class ∪ 𝑘 | 
| 16 | 11 | cuni 3839 | 
. . . . 5
class ∪ 𝑗 | 
| 17 |   | cmap 6707 | 
. . . . 5
class 
↑𝑚 | 
| 18 | 15, 16, 17 | co 5922 | 
. . . 4
class (∪ 𝑘
↑𝑚 ∪ 𝑗) | 
| 19 | 14, 5, 18 | crab 2479 | 
. . 3
class {𝑓 ∈ (∪ 𝑘
↑𝑚 ∪ 𝑗) ∣ ∀𝑦 ∈ 𝑘 (◡𝑓 “ 𝑦) ∈ 𝑗} | 
| 20 | 2, 3, 4, 4, 19 | cmpo 5924 | 
. 2
class (𝑗 ∈ Top, 𝑘 ∈ Top ↦ {𝑓 ∈ (∪ 𝑘 ↑𝑚
∪ 𝑗) ∣ ∀𝑦 ∈ 𝑘 (◡𝑓 “ 𝑦) ∈ 𝑗}) | 
| 21 | 1, 20 | wceq 1364 | 
1
wff  Cn =
(𝑗 ∈ Top, 𝑘 ∈ Top ↦ {𝑓 ∈ (∪ 𝑘
↑𝑚 ∪ 𝑗) ∣ ∀𝑦 ∈ 𝑘 (◡𝑓 “ 𝑦) ∈ 𝑗}) |