| Step | Hyp | Ref | Expression | 
						
							| 1 |  | bdayelon |  | 
						
							| 2 | 1 | onordi |  | 
						
							| 3 |  | bdayelon |  | 
						
							| 4 | 3 | onordi |  | 
						
							| 5 |  | ordtri2or |  | 
						
							| 6 | 2 4 5 | mp2an |  | 
						
							| 7 | 6 | a1i |  | 
						
							| 8 |  | madeun |  | 
						
							| 9 | 8 | eleq2i |  | 
						
							| 10 |  | elun |  | 
						
							| 11 | 9 10 | bitri |  | 
						
							| 12 |  | lrold |  | 
						
							| 13 | 12 | eleq2i |  | 
						
							| 14 |  | elons |  | 
						
							| 15 | 14 | simprbi |  | 
						
							| 16 | 15 | adantl |  | 
						
							| 17 | 16 | uneq2d |  | 
						
							| 18 |  | un0 |  | 
						
							| 19 | 17 18 | eqtrdi |  | 
						
							| 20 | 19 | eleq2d |  | 
						
							| 21 |  | simpll |  | 
						
							| 22 |  | onsno |  | 
						
							| 23 | 22 | ad2antlr |  | 
						
							| 24 |  | breq1 | Could not format  ( xO = A -> ( xO  A  ( xO  A 
						 | 
						
							| 25 |  | leftval | Could not format  ( _Left ` x ) = { xO e. ( _Old ` ( bday ` x ) ) | xO 
						 | 
						
							| 26 | 24 25 | elrab2 |  | 
						
							| 27 | 26 | simprbi |  | 
						
							| 28 | 27 | adantl |  | 
						
							| 29 | 21 23 28 | sltled |  | 
						
							| 30 | 29 | ex |  | 
						
							| 31 | 20 30 | sylbid |  | 
						
							| 32 | 13 31 | biimtrrid |  | 
						
							| 33 |  | newbday |  | 
						
							| 34 | 1 33 | mpan |  | 
						
							| 35 | 34 | adantr |  | 
						
							| 36 |  | leftssold |  | 
						
							| 37 |  | fveq2 |  | 
						
							| 38 | 37 | adantl |  | 
						
							| 39 | 15 | uneq2d |  | 
						
							| 40 | 39 12 18 | 3eqtr3g |  | 
						
							| 41 | 40 | ad2antlr |  | 
						
							| 42 | 38 41 | eqtr2d |  | 
						
							| 43 | 36 42 | sseqtrrid |  | 
						
							| 44 |  | slelss |  | 
						
							| 45 | 22 44 | syl3an2 |  | 
						
							| 46 | 45 | 3expa |  | 
						
							| 47 | 43 46 | mpbird |  | 
						
							| 48 | 47 | ex |  | 
						
							| 49 | 35 48 | sylbid |  | 
						
							| 50 | 32 49 | jaod |  | 
						
							| 51 | 11 50 | biimtrid |  | 
						
							| 52 |  | madebday |  | 
						
							| 53 | 1 52 | mpan |  | 
						
							| 54 | 53 | adantr |  | 
						
							| 55 |  | slenlt |  | 
						
							| 56 | 22 55 | sylan2 |  | 
						
							| 57 | 51 54 56 | 3imtr3d |  | 
						
							| 58 | 57 | con2d |  | 
						
							| 59 | 58 | 3impia |  | 
						
							| 60 | 7 59 | olcnd |  | 
						
							| 61 | 22 | 3ad2ant2 |  | 
						
							| 62 |  | oldbday |  | 
						
							| 63 | 3 61 62 | sylancr |  | 
						
							| 64 | 60 63 | mpbird |  | 
						
							| 65 | 64 | rabssdv |  |