Metamath Proof Explorer


Theorem cflim2

Description: The cofinality function is a limit ordinal iff its argument is. (Contributed by Mario Carneiro, 28-Feb-2013) (Revised by Mario Carneiro, 15-Sep-2013)

Ref Expression
Hypothesis cflim2.1 𝐴 ∈ V
Assertion cflim2 ( Lim 𝐴 ↔ Lim ( cf ‘ 𝐴 ) )

Proof

Step Hyp Ref Expression
1 cflim2.1 𝐴 ∈ V
2 rabid ( 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ↔ ( 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 ) )
3 velpw ( 𝑦 ∈ 𝒫 𝐴𝑦𝐴 )
4 limord ( Lim 𝐴 → Ord 𝐴 )
5 ordsson ( Ord 𝐴𝐴 ⊆ On )
6 sstr ( ( 𝑦𝐴𝐴 ⊆ On ) → 𝑦 ⊆ On )
7 6 expcom ( 𝐴 ⊆ On → ( 𝑦𝐴𝑦 ⊆ On ) )
8 4 5 7 3syl ( Lim 𝐴 → ( 𝑦𝐴𝑦 ⊆ On ) )
9 8 imp ( ( Lim 𝐴𝑦𝐴 ) → 𝑦 ⊆ On )
10 9 3adant3 ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → 𝑦 ⊆ On )
11 ssel2 ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) → 𝑠 ∈ On )
12 eloni ( 𝑠 ∈ On → Ord 𝑠 )
13 ordirr ( Ord 𝑠 → ¬ 𝑠𝑠 )
14 11 12 13 3syl ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) → ¬ 𝑠𝑠 )
15 ssel ( 𝑦𝑠 → ( 𝑠𝑦𝑠𝑠 ) )
16 15 com12 ( 𝑠𝑦 → ( 𝑦𝑠𝑠𝑠 ) )
17 16 adantl ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) → ( 𝑦𝑠𝑠𝑠 ) )
18 14 17 mtod ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) → ¬ 𝑦𝑠 )
19 10 18 sylan ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → ¬ 𝑦𝑠 )
20 simpl2 ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → 𝑦𝐴 )
21 sstr ( ( 𝑦𝐴𝐴𝑠 ) → 𝑦𝑠 )
22 20 21 sylan ( ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) ∧ 𝐴𝑠 ) → 𝑦𝑠 )
23 19 22 mtand ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → ¬ 𝐴𝑠 )
24 simpl3 ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → 𝑦 = 𝐴 )
25 24 sseq1d ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → ( 𝑦𝑠𝐴𝑠 ) )
26 23 25 mtbird ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → ¬ 𝑦𝑠 )
27 unissb ( 𝑦𝑠 ↔ ∀ 𝑡𝑦 𝑡𝑠 )
28 26 27 sylnib ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ 𝑠𝑦 ) → ¬ ∀ 𝑡𝑦 𝑡𝑠 )
29 28 nrexdv ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → ¬ ∃ 𝑠𝑦𝑡𝑦 𝑡𝑠 )
30 ssel ( 𝑦 ⊆ On → ( 𝑠𝑦𝑠 ∈ On ) )
31 ssel ( 𝑦 ⊆ On → ( 𝑡𝑦𝑡 ∈ On ) )
32 ontri1 ( ( 𝑡 ∈ On ∧ 𝑠 ∈ On ) → ( 𝑡𝑠 ↔ ¬ 𝑠𝑡 ) )
33 32 ancoms ( ( 𝑠 ∈ On ∧ 𝑡 ∈ On ) → ( 𝑡𝑠 ↔ ¬ 𝑠𝑡 ) )
34 vex 𝑡 ∈ V
35 vex 𝑠 ∈ V
36 34 35 brcnv ( 𝑡 E 𝑠𝑠 E 𝑡 )
37 epel ( 𝑠 E 𝑡𝑠𝑡 )
38 36 37 bitri ( 𝑡 E 𝑠𝑠𝑡 )
39 38 notbii ( ¬ 𝑡 E 𝑠 ↔ ¬ 𝑠𝑡 )
40 33 39 bitr4di ( ( 𝑠 ∈ On ∧ 𝑡 ∈ On ) → ( 𝑡𝑠 ↔ ¬ 𝑡 E 𝑠 ) )
41 40 a1i ( 𝑦 ⊆ On → ( ( 𝑠 ∈ On ∧ 𝑡 ∈ On ) → ( 𝑡𝑠 ↔ ¬ 𝑡 E 𝑠 ) ) )
42 30 31 41 syl2and ( 𝑦 ⊆ On → ( ( 𝑠𝑦𝑡𝑦 ) → ( 𝑡𝑠 ↔ ¬ 𝑡 E 𝑠 ) ) )
43 42 impl ( ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) ∧ 𝑡𝑦 ) → ( 𝑡𝑠 ↔ ¬ 𝑡 E 𝑠 ) )
44 43 ralbidva ( ( 𝑦 ⊆ On ∧ 𝑠𝑦 ) → ( ∀ 𝑡𝑦 𝑡𝑠 ↔ ∀ 𝑡𝑦 ¬ 𝑡 E 𝑠 ) )
45 44 rexbidva ( 𝑦 ⊆ On → ( ∃ 𝑠𝑦𝑡𝑦 𝑡𝑠 ↔ ∃ 𝑠𝑦𝑡𝑦 ¬ 𝑡 E 𝑠 ) )
46 10 45 syl ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → ( ∃ 𝑠𝑦𝑡𝑦 𝑡𝑠 ↔ ∃ 𝑠𝑦𝑡𝑦 ¬ 𝑡 E 𝑠 ) )
47 29 46 mtbid ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → ¬ ∃ 𝑠𝑦𝑡𝑦 ¬ 𝑡 E 𝑠 )
48 vex 𝑦 ∈ V
49 48 a1i ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → 𝑦 ∈ V )
50 epweon E We On
51 wess ( 𝑦 ⊆ On → ( E We On → E We 𝑦 ) )
52 50 51 mpi ( 𝑦 ⊆ On → E We 𝑦 )
53 weso ( E We 𝑦 → E Or 𝑦 )
54 52 53 syl ( 𝑦 ⊆ On → E Or 𝑦 )
55 cnvso ( E Or 𝑦 E Or 𝑦 )
56 54 55 sylib ( 𝑦 ⊆ On → E Or 𝑦 )
57 onssnum ( ( 𝑦 ∈ V ∧ 𝑦 ⊆ On ) → 𝑦 ∈ dom card )
58 48 57 mpan ( 𝑦 ⊆ On → 𝑦 ∈ dom card )
59 cardid2 ( 𝑦 ∈ dom card → ( card ‘ 𝑦 ) ≈ 𝑦 )
60 ensym ( ( card ‘ 𝑦 ) ≈ 𝑦𝑦 ≈ ( card ‘ 𝑦 ) )
61 58 59 60 3syl ( 𝑦 ⊆ On → 𝑦 ≈ ( card ‘ 𝑦 ) )
62 nnsdom ( ( card ‘ 𝑦 ) ∈ ω → ( card ‘ 𝑦 ) ≺ ω )
63 ensdomtr ( ( 𝑦 ≈ ( card ‘ 𝑦 ) ∧ ( card ‘ 𝑦 ) ≺ ω ) → 𝑦 ≺ ω )
64 61 62 63 syl2an ( ( 𝑦 ⊆ On ∧ ( card ‘ 𝑦 ) ∈ ω ) → 𝑦 ≺ ω )
65 isfinite ( 𝑦 ∈ Fin ↔ 𝑦 ≺ ω )
66 64 65 sylibr ( ( 𝑦 ⊆ On ∧ ( card ‘ 𝑦 ) ∈ ω ) → 𝑦 ∈ Fin )
67 wofi ( ( E Or 𝑦𝑦 ∈ Fin ) → E We 𝑦 )
68 56 66 67 syl2an2r ( ( 𝑦 ⊆ On ∧ ( card ‘ 𝑦 ) ∈ ω ) → E We 𝑦 )
69 10 68 sylan ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → E We 𝑦 )
70 wefr ( E We 𝑦 E Fr 𝑦 )
71 69 70 syl ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → E Fr 𝑦 )
72 ssidd ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → 𝑦𝑦 )
73 unieq ( 𝑦 = ∅ → 𝑦 = ∅ )
74 uni0 ∅ = ∅
75 73 74 eqtrdi ( 𝑦 = ∅ → 𝑦 = ∅ )
76 eqeq1 ( 𝑦 = 𝐴 → ( 𝑦 = ∅ ↔ 𝐴 = ∅ ) )
77 75 76 syl5ib ( 𝑦 = 𝐴 → ( 𝑦 = ∅ → 𝐴 = ∅ ) )
78 nlim0 ¬ Lim ∅
79 limeq ( 𝐴 = ∅ → ( Lim 𝐴 ↔ Lim ∅ ) )
80 78 79 mtbiri ( 𝐴 = ∅ → ¬ Lim 𝐴 )
81 77 80 syl6 ( 𝑦 = 𝐴 → ( 𝑦 = ∅ → ¬ Lim 𝐴 ) )
82 81 necon2ad ( 𝑦 = 𝐴 → ( Lim 𝐴𝑦 ≠ ∅ ) )
83 82 impcom ( ( Lim 𝐴 𝑦 = 𝐴 ) → 𝑦 ≠ ∅ )
84 83 3adant2 ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → 𝑦 ≠ ∅ )
85 84 adantr ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → 𝑦 ≠ ∅ )
86 fri ( ( ( 𝑦 ∈ V ∧ E Fr 𝑦 ) ∧ ( 𝑦𝑦𝑦 ≠ ∅ ) ) → ∃ 𝑠𝑦𝑡𝑦 ¬ 𝑡 E 𝑠 )
87 49 71 72 85 86 syl22anc ( ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) ∧ ( card ‘ 𝑦 ) ∈ ω ) → ∃ 𝑠𝑦𝑡𝑦 ¬ 𝑡 E 𝑠 )
88 47 87 mtand ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → ¬ ( card ‘ 𝑦 ) ∈ ω )
89 cardon ( card ‘ 𝑦 ) ∈ On
90 eloni ( ( card ‘ 𝑦 ) ∈ On → Ord ( card ‘ 𝑦 ) )
91 ordom Ord ω
92 ordtri1 ( ( Ord ω ∧ Ord ( card ‘ 𝑦 ) ) → ( ω ⊆ ( card ‘ 𝑦 ) ↔ ¬ ( card ‘ 𝑦 ) ∈ ω ) )
93 91 92 mpan ( Ord ( card ‘ 𝑦 ) → ( ω ⊆ ( card ‘ 𝑦 ) ↔ ¬ ( card ‘ 𝑦 ) ∈ ω ) )
94 89 90 93 mp2b ( ω ⊆ ( card ‘ 𝑦 ) ↔ ¬ ( card ‘ 𝑦 ) ∈ ω )
95 88 94 sylibr ( ( Lim 𝐴𝑦𝐴 𝑦 = 𝐴 ) → ω ⊆ ( card ‘ 𝑦 ) )
96 3 95 syl3an2b ( ( Lim 𝐴𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 ) → ω ⊆ ( card ‘ 𝑦 ) )
97 96 3expb ( ( Lim 𝐴 ∧ ( 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 ) ) → ω ⊆ ( card ‘ 𝑦 ) )
98 2 97 sylan2b ( ( Lim 𝐴𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ) → ω ⊆ ( card ‘ 𝑦 ) )
99 98 ralrimiva ( Lim 𝐴 → ∀ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ω ⊆ ( card ‘ 𝑦 ) )
100 ssiin ( ω ⊆ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ( card ‘ 𝑦 ) ↔ ∀ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ω ⊆ ( card ‘ 𝑦 ) )
101 99 100 sylibr ( Lim 𝐴 → ω ⊆ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ( card ‘ 𝑦 ) )
102 1 cflim3 ( Lim 𝐴 → ( cf ‘ 𝐴 ) = 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ( card ‘ 𝑦 ) )
103 101 102 sseqtrrd ( Lim 𝐴 → ω ⊆ ( cf ‘ 𝐴 ) )
104 fvex ( card ‘ 𝑦 ) ∈ V
105 104 dfiin2 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } ( card ‘ 𝑦 ) = { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) }
106 102 105 eqtrdi ( Lim 𝐴 → ( cf ‘ 𝐴 ) = { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } )
107 cardlim ( ω ⊆ ( card ‘ 𝑦 ) ↔ Lim ( card ‘ 𝑦 ) )
108 sseq2 ( 𝑥 = ( card ‘ 𝑦 ) → ( ω ⊆ 𝑥 ↔ ω ⊆ ( card ‘ 𝑦 ) ) )
109 limeq ( 𝑥 = ( card ‘ 𝑦 ) → ( Lim 𝑥 ↔ Lim ( card ‘ 𝑦 ) ) )
110 108 109 bibi12d ( 𝑥 = ( card ‘ 𝑦 ) → ( ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) ↔ ( ω ⊆ ( card ‘ 𝑦 ) ↔ Lim ( card ‘ 𝑦 ) ) ) )
111 107 110 mpbiri ( 𝑥 = ( card ‘ 𝑦 ) → ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) )
112 111 rexlimivw ( ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) → ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) )
113 112 ss2abi { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ⊆ { 𝑥 ∣ ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) }
114 eleq1 ( 𝑥 = ( card ‘ 𝑦 ) → ( 𝑥 ∈ On ↔ ( card ‘ 𝑦 ) ∈ On ) )
115 89 114 mpbiri ( 𝑥 = ( card ‘ 𝑦 ) → 𝑥 ∈ On )
116 115 rexlimivw ( ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) → 𝑥 ∈ On )
117 116 abssi { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ⊆ On
118 fvex ( cf ‘ 𝐴 ) ∈ V
119 106 118 eqeltrrdi ( Lim 𝐴 { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ∈ V )
120 intex ( { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ≠ ∅ ↔ { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ∈ V )
121 119 120 sylibr ( Lim 𝐴 → { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ≠ ∅ )
122 onint ( ( { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ⊆ On ∧ { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ≠ ∅ ) → { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ∈ { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } )
123 117 121 122 sylancr ( Lim 𝐴 { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ∈ { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } )
124 113 123 sselid ( Lim 𝐴 { 𝑥 ∣ ∃ 𝑦 ∈ { 𝑦 ∈ 𝒫 𝐴 𝑦 = 𝐴 } 𝑥 = ( card ‘ 𝑦 ) } ∈ { 𝑥 ∣ ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) } )
125 106 124 eqeltrd ( Lim 𝐴 → ( cf ‘ 𝐴 ) ∈ { 𝑥 ∣ ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) } )
126 sseq2 ( 𝑥 = ( cf ‘ 𝐴 ) → ( ω ⊆ 𝑥 ↔ ω ⊆ ( cf ‘ 𝐴 ) ) )
127 limeq ( 𝑥 = ( cf ‘ 𝐴 ) → ( Lim 𝑥 ↔ Lim ( cf ‘ 𝐴 ) ) )
128 126 127 bibi12d ( 𝑥 = ( cf ‘ 𝐴 ) → ( ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) ↔ ( ω ⊆ ( cf ‘ 𝐴 ) ↔ Lim ( cf ‘ 𝐴 ) ) ) )
129 118 128 elab ( ( cf ‘ 𝐴 ) ∈ { 𝑥 ∣ ( ω ⊆ 𝑥 ↔ Lim 𝑥 ) } ↔ ( ω ⊆ ( cf ‘ 𝐴 ) ↔ Lim ( cf ‘ 𝐴 ) ) )
130 125 129 sylib ( Lim 𝐴 → ( ω ⊆ ( cf ‘ 𝐴 ) ↔ Lim ( cf ‘ 𝐴 ) ) )
131 103 130 mpbid ( Lim 𝐴 → Lim ( cf ‘ 𝐴 ) )
132 eloni ( 𝐴 ∈ On → Ord 𝐴 )
133 ordzsl ( Ord 𝐴 ↔ ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ∨ Lim 𝐴 ) )
134 132 133 sylib ( 𝐴 ∈ On → ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ∨ Lim 𝐴 ) )
135 df-3or ( ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ∨ Lim 𝐴 ) ↔ ( ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ∨ Lim 𝐴 ) )
136 orcom ( ( ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ∨ Lim 𝐴 ) ↔ ( Lim 𝐴 ∨ ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ) )
137 df-or ( ( Lim 𝐴 ∨ ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ) ↔ ( ¬ Lim 𝐴 → ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ) )
138 135 136 137 3bitri ( ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ∨ Lim 𝐴 ) ↔ ( ¬ Lim 𝐴 → ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ) )
139 134 138 sylib ( 𝐴 ∈ On → ( ¬ Lim 𝐴 → ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) ) )
140 fveq2 ( 𝐴 = ∅ → ( cf ‘ 𝐴 ) = ( cf ‘ ∅ ) )
141 cf0 ( cf ‘ ∅ ) = ∅
142 140 141 eqtrdi ( 𝐴 = ∅ → ( cf ‘ 𝐴 ) = ∅ )
143 limeq ( ( cf ‘ 𝐴 ) = ∅ → ( Lim ( cf ‘ 𝐴 ) ↔ Lim ∅ ) )
144 142 143 syl ( 𝐴 = ∅ → ( Lim ( cf ‘ 𝐴 ) ↔ Lim ∅ ) )
145 78 144 mtbiri ( 𝐴 = ∅ → ¬ Lim ( cf ‘ 𝐴 ) )
146 1n0 1o ≠ ∅
147 df1o2 1o = { ∅ }
148 147 unieqi 1o = { ∅ }
149 0ex ∅ ∈ V
150 149 unisn { ∅ } = ∅
151 148 150 eqtri 1o = ∅
152 146 151 neeqtrri 1o 1o
153 limuni ( Lim 1o → 1o = 1o )
154 153 necon3ai ( 1o 1o → ¬ Lim 1o )
155 152 154 ax-mp ¬ Lim 1o
156 fveq2 ( 𝐴 = suc 𝑥 → ( cf ‘ 𝐴 ) = ( cf ‘ suc 𝑥 ) )
157 cfsuc ( 𝑥 ∈ On → ( cf ‘ suc 𝑥 ) = 1o )
158 156 157 sylan9eqr ( ( 𝑥 ∈ On ∧ 𝐴 = suc 𝑥 ) → ( cf ‘ 𝐴 ) = 1o )
159 limeq ( ( cf ‘ 𝐴 ) = 1o → ( Lim ( cf ‘ 𝐴 ) ↔ Lim 1o ) )
160 158 159 syl ( ( 𝑥 ∈ On ∧ 𝐴 = suc 𝑥 ) → ( Lim ( cf ‘ 𝐴 ) ↔ Lim 1o ) )
161 155 160 mtbiri ( ( 𝑥 ∈ On ∧ 𝐴 = suc 𝑥 ) → ¬ Lim ( cf ‘ 𝐴 ) )
162 161 rexlimiva ( ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 → ¬ Lim ( cf ‘ 𝐴 ) )
163 145 162 jaoi ( ( 𝐴 = ∅ ∨ ∃ 𝑥 ∈ On 𝐴 = suc 𝑥 ) → ¬ Lim ( cf ‘ 𝐴 ) )
164 139 163 syl6 ( 𝐴 ∈ On → ( ¬ Lim 𝐴 → ¬ Lim ( cf ‘ 𝐴 ) ) )
165 164 con4d ( 𝐴 ∈ On → ( Lim ( cf ‘ 𝐴 ) → Lim 𝐴 ) )
166 cff cf : On ⟶ On
167 166 fdmi dom cf = On
168 167 eleq2i ( 𝐴 ∈ dom cf ↔ 𝐴 ∈ On )
169 ndmfv ( ¬ 𝐴 ∈ dom cf → ( cf ‘ 𝐴 ) = ∅ )
170 168 169 sylnbir ( ¬ 𝐴 ∈ On → ( cf ‘ 𝐴 ) = ∅ )
171 170 143 syl ( ¬ 𝐴 ∈ On → ( Lim ( cf ‘ 𝐴 ) ↔ Lim ∅ ) )
172 78 171 mtbiri ( ¬ 𝐴 ∈ On → ¬ Lim ( cf ‘ 𝐴 ) )
173 172 pm2.21d ( ¬ 𝐴 ∈ On → ( Lim ( cf ‘ 𝐴 ) → Lim 𝐴 ) )
174 165 173 pm2.61i ( Lim ( cf ‘ 𝐴 ) → Lim 𝐴 )
175 131 174 impbii ( Lim 𝐴 ↔ Lim ( cf ‘ 𝐴 ) )