| Step | Hyp | Ref | Expression | 
						
							| 1 |  | xpsinv.t |  |-  T = ( R Xs. S ) | 
						
							| 2 |  | xpsinv.x |  |-  X = ( Base ` R ) | 
						
							| 3 |  | xpsinv.y |  |-  Y = ( Base ` S ) | 
						
							| 4 |  | xpsinv.r |  |-  ( ph -> R e. Grp ) | 
						
							| 5 |  | xpsinv.s |  |-  ( ph -> S e. Grp ) | 
						
							| 6 |  | xpsinv.a |  |-  ( ph -> A e. X ) | 
						
							| 7 |  | xpsinv.b |  |-  ( ph -> B e. Y ) | 
						
							| 8 |  | xpsinv.m |  |-  M = ( invg ` R ) | 
						
							| 9 |  | xpsinv.n |  |-  N = ( invg ` S ) | 
						
							| 10 |  | xpsinv.i |  |-  I = ( invg ` T ) | 
						
							| 11 |  | eqid |  |-  ( +g ` R ) = ( +g ` R ) | 
						
							| 12 |  | eqid |  |-  ( 0g ` R ) = ( 0g ` R ) | 
						
							| 13 | 2 11 12 8 4 6 | grplinvd |  |-  ( ph -> ( ( M ` A ) ( +g ` R ) A ) = ( 0g ` R ) ) | 
						
							| 14 |  | eqid |  |-  ( +g ` S ) = ( +g ` S ) | 
						
							| 15 |  | eqid |  |-  ( 0g ` S ) = ( 0g ` S ) | 
						
							| 16 | 3 14 15 9 5 7 | grplinvd |  |-  ( ph -> ( ( N ` B ) ( +g ` S ) B ) = ( 0g ` S ) ) | 
						
							| 17 | 13 16 | opeq12d |  |-  ( ph -> <. ( ( M ` A ) ( +g ` R ) A ) , ( ( N ` B ) ( +g ` S ) B ) >. = <. ( 0g ` R ) , ( 0g ` S ) >. ) | 
						
							| 18 | 2 8 4 6 | grpinvcld |  |-  ( ph -> ( M ` A ) e. X ) | 
						
							| 19 | 3 9 5 7 | grpinvcld |  |-  ( ph -> ( N ` B ) e. Y ) | 
						
							| 20 | 2 11 4 18 6 | grpcld |  |-  ( ph -> ( ( M ` A ) ( +g ` R ) A ) e. X ) | 
						
							| 21 | 3 14 5 19 7 | grpcld |  |-  ( ph -> ( ( N ` B ) ( +g ` S ) B ) e. Y ) | 
						
							| 22 |  | eqid |  |-  ( +g ` T ) = ( +g ` T ) | 
						
							| 23 | 1 2 3 4 5 18 19 6 7 20 21 11 14 22 | xpsadd |  |-  ( ph -> ( <. ( M ` A ) , ( N ` B ) >. ( +g ` T ) <. A , B >. ) = <. ( ( M ` A ) ( +g ` R ) A ) , ( ( N ` B ) ( +g ` S ) B ) >. ) | 
						
							| 24 | 4 | grpmndd |  |-  ( ph -> R e. Mnd ) | 
						
							| 25 | 5 | grpmndd |  |-  ( ph -> S e. Mnd ) | 
						
							| 26 | 1 | xpsmnd0 |  |-  ( ( R e. Mnd /\ S e. Mnd ) -> ( 0g ` T ) = <. ( 0g ` R ) , ( 0g ` S ) >. ) | 
						
							| 27 | 24 25 26 | syl2anc |  |-  ( ph -> ( 0g ` T ) = <. ( 0g ` R ) , ( 0g ` S ) >. ) | 
						
							| 28 | 17 23 27 | 3eqtr4d |  |-  ( ph -> ( <. ( M ` A ) , ( N ` B ) >. ( +g ` T ) <. A , B >. ) = ( 0g ` T ) ) | 
						
							| 29 | 1 | xpsgrp |  |-  ( ( R e. Grp /\ S e. Grp ) -> T e. Grp ) | 
						
							| 30 | 4 5 29 | syl2anc |  |-  ( ph -> T e. Grp ) | 
						
							| 31 | 6 7 | opelxpd |  |-  ( ph -> <. A , B >. e. ( X X. Y ) ) | 
						
							| 32 | 1 2 3 4 5 | xpsbas |  |-  ( ph -> ( X X. Y ) = ( Base ` T ) ) | 
						
							| 33 | 31 32 | eleqtrd |  |-  ( ph -> <. A , B >. e. ( Base ` T ) ) | 
						
							| 34 | 18 19 | opelxpd |  |-  ( ph -> <. ( M ` A ) , ( N ` B ) >. e. ( X X. Y ) ) | 
						
							| 35 | 34 32 | eleqtrd |  |-  ( ph -> <. ( M ` A ) , ( N ` B ) >. e. ( Base ` T ) ) | 
						
							| 36 |  | eqid |  |-  ( Base ` T ) = ( Base ` T ) | 
						
							| 37 |  | eqid |  |-  ( 0g ` T ) = ( 0g ` T ) | 
						
							| 38 | 36 22 37 10 | grpinvid2 |  |-  ( ( T e. Grp /\ <. A , B >. e. ( Base ` T ) /\ <. ( M ` A ) , ( N ` B ) >. e. ( Base ` T ) ) -> ( ( I ` <. A , B >. ) = <. ( M ` A ) , ( N ` B ) >. <-> ( <. ( M ` A ) , ( N ` B ) >. ( +g ` T ) <. A , B >. ) = ( 0g ` T ) ) ) | 
						
							| 39 | 30 33 35 38 | syl3anc |  |-  ( ph -> ( ( I ` <. A , B >. ) = <. ( M ` A ) , ( N ` B ) >. <-> ( <. ( M ` A ) , ( N ` B ) >. ( +g ` T ) <. A , B >. ) = ( 0g ` T ) ) ) | 
						
							| 40 | 28 39 | mpbird |  |-  ( ph -> ( I ` <. A , B >. ) = <. ( M ` A ) , ( N ` B ) >. ) |