| Step | Hyp | Ref | Expression | 
						
							| 1 |  | onfin2 | ⊢ ω  =  ( On  ∩  Fin ) | 
						
							| 2 |  | inss2 | ⊢ ( On  ∩  Fin )  ⊆  Fin | 
						
							| 3 | 1 2 | eqsstri | ⊢ ω  ⊆  Fin | 
						
							| 4 |  | peano2 | ⊢ ( 𝐴  ∈  ω  →  suc  𝐴  ∈  ω ) | 
						
							| 5 | 3 4 | sselid | ⊢ ( 𝐴  ∈  ω  →  suc  𝐴  ∈  Fin ) | 
						
							| 6 | 5 | 3ad2ant3 | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  suc  𝐴  ∈  Fin ) | 
						
							| 7 | 4 | 3ad2ant3 | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  suc  𝐴  ∈  ω ) | 
						
							| 8 |  | breq1 | ⊢ ( 𝑏  =  𝑐  →  ( 𝑏  ≼  𝐴  ↔  𝑐  ≼  𝐴 ) ) | 
						
							| 9 | 8 | elrab | ⊢ ( 𝑐  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ↔  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) ) | 
						
							| 10 |  | simprr | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝑐  ≼  𝐴 ) | 
						
							| 11 |  | simpl2 | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝑋  ⊆  Fin ) | 
						
							| 12 |  | simprl | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝑐  ∈  𝑋 ) | 
						
							| 13 | 11 12 | sseldd | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝑐  ∈  Fin ) | 
						
							| 14 |  | finnum | ⊢ ( 𝑐  ∈  Fin  →  𝑐  ∈  dom  card ) | 
						
							| 15 | 13 14 | syl | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝑐  ∈  dom  card ) | 
						
							| 16 |  | simpl3 | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝐴  ∈  ω ) | 
						
							| 17 | 3 16 | sselid | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝐴  ∈  Fin ) | 
						
							| 18 |  | finnum | ⊢ ( 𝐴  ∈  Fin  →  𝐴  ∈  dom  card ) | 
						
							| 19 | 17 18 | syl | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  𝐴  ∈  dom  card ) | 
						
							| 20 |  | carddom2 | ⊢ ( ( 𝑐  ∈  dom  card  ∧  𝐴  ∈  dom  card )  →  ( ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 )  ↔  𝑐  ≼  𝐴 ) ) | 
						
							| 21 | 15 19 20 | syl2anc | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  ( ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 )  ↔  𝑐  ≼  𝐴 ) ) | 
						
							| 22 | 10 21 | mpbird | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 ) )  →  ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 ) ) | 
						
							| 23 | 22 | ex | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 )  →  ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 ) ) ) | 
						
							| 24 |  | cardnn | ⊢ ( 𝐴  ∈  ω  →  ( card ‘ 𝐴 )  =  𝐴 ) | 
						
							| 25 | 24 | sseq2d | ⊢ ( 𝐴  ∈  ω  →  ( ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 )  ↔  ( card ‘ 𝑐 )  ⊆  𝐴 ) ) | 
						
							| 26 |  | cardon | ⊢ ( card ‘ 𝑐 )  ∈  On | 
						
							| 27 |  | nnon | ⊢ ( 𝐴  ∈  ω  →  𝐴  ∈  On ) | 
						
							| 28 |  | onsssuc | ⊢ ( ( ( card ‘ 𝑐 )  ∈  On  ∧  𝐴  ∈  On )  →  ( ( card ‘ 𝑐 )  ⊆  𝐴  ↔  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 29 | 26 27 28 | sylancr | ⊢ ( 𝐴  ∈  ω  →  ( ( card ‘ 𝑐 )  ⊆  𝐴  ↔  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 30 | 25 29 | bitrd | ⊢ ( 𝐴  ∈  ω  →  ( ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 )  ↔  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 31 | 30 | 3ad2ant3 | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( ( card ‘ 𝑐 )  ⊆  ( card ‘ 𝐴 )  ↔  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 32 | 23 31 | sylibd | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( ( 𝑐  ∈  𝑋  ∧  𝑐  ≼  𝐴 )  →  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 33 | 9 32 | biimtrid | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( 𝑐  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  →  ( card ‘ 𝑐 )  ∈  suc  𝐴 ) ) | 
						
							| 34 |  | elrabi | ⊢ ( 𝑐  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  →  𝑐  ∈  𝑋 ) | 
						
							| 35 |  | elrabi | ⊢ ( 𝑑  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  →  𝑑  ∈  𝑋 ) | 
						
							| 36 |  | ssel | ⊢ ( 𝑋  ⊆  Fin  →  ( 𝑐  ∈  𝑋  →  𝑐  ∈  Fin ) ) | 
						
							| 37 |  | ssel | ⊢ ( 𝑋  ⊆  Fin  →  ( 𝑑  ∈  𝑋  →  𝑑  ∈  Fin ) ) | 
						
							| 38 | 36 37 | anim12d | ⊢ ( 𝑋  ⊆  Fin  →  ( ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 )  →  ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin ) ) ) | 
						
							| 39 | 38 | imp | ⊢ ( ( 𝑋  ⊆  Fin  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin ) ) | 
						
							| 40 | 39 | 3ad2antl2 | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin ) ) | 
						
							| 41 |  | sorpssi | ⊢ ( (  [⊊]   Or  𝑋  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) ) | 
						
							| 42 | 41 | 3ad2antl1 | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) ) | 
						
							| 43 |  | finnum | ⊢ ( 𝑑  ∈  Fin  →  𝑑  ∈  dom  card ) | 
						
							| 44 |  | carden2 | ⊢ ( ( 𝑐  ∈  dom  card  ∧  𝑑  ∈  dom  card )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  ≈  𝑑 ) ) | 
						
							| 45 | 14 43 44 | syl2an | ⊢ ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  ≈  𝑑 ) ) | 
						
							| 46 | 45 | adantr | ⊢ ( ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin )  ∧  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  ≈  𝑑 ) ) | 
						
							| 47 |  | fin23lem25 | ⊢ ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin  ∧  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) )  →  ( 𝑐  ≈  𝑑  ↔  𝑐  =  𝑑 ) ) | 
						
							| 48 | 47 | 3expa | ⊢ ( ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin )  ∧  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) )  →  ( 𝑐  ≈  𝑑  ↔  𝑐  =  𝑑 ) ) | 
						
							| 49 | 48 | biimpd | ⊢ ( ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin )  ∧  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) )  →  ( 𝑐  ≈  𝑑  →  𝑐  =  𝑑 ) ) | 
						
							| 50 | 46 49 | sylbid | ⊢ ( ( ( 𝑐  ∈  Fin  ∧  𝑑  ∈  Fin )  ∧  ( 𝑐  ⊆  𝑑  ∨  𝑑  ⊆  𝑐 ) )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  →  𝑐  =  𝑑 ) ) | 
						
							| 51 | 40 42 50 | syl2anc | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  →  𝑐  =  𝑑 ) ) | 
						
							| 52 |  | fveq2 | ⊢ ( 𝑐  =  𝑑  →  ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 ) ) | 
						
							| 53 | 51 52 | impbid1 | ⊢ ( ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  ∧  ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 ) )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  =  𝑑 ) ) | 
						
							| 54 | 53 | ex | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( ( 𝑐  ∈  𝑋  ∧  𝑑  ∈  𝑋 )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  =  𝑑 ) ) ) | 
						
							| 55 | 34 35 54 | syl2ani | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( ( 𝑐  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ∧  𝑑  ∈  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 } )  →  ( ( card ‘ 𝑐 )  =  ( card ‘ 𝑑 )  ↔  𝑐  =  𝑑 ) ) ) | 
						
							| 56 | 33 55 | dom2d | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  ( suc  𝐴  ∈  ω  →  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ≼  suc  𝐴 ) ) | 
						
							| 57 | 7 56 | mpd | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ≼  suc  𝐴 ) | 
						
							| 58 |  | domfi | ⊢ ( ( suc  𝐴  ∈  Fin  ∧  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ≼  suc  𝐴 )  →  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ∈  Fin ) | 
						
							| 59 | 6 57 58 | syl2anc | ⊢ ( (  [⊊]   Or  𝑋  ∧  𝑋  ⊆  Fin  ∧  𝐴  ∈  ω )  →  { 𝑏  ∈  𝑋  ∣  𝑏  ≼  𝐴 }  ∈  Fin ) |