let X be ARS ; :: thesis: for x, y being Element of X holds
( x >>01<< y iff x,y are_convergent<=1_wrt the reduction of X )
let x, y be Element of X; :: thesis: ( x >>01<< y iff x,y are_convergent<=1_wrt the reduction of X )
set R = the reduction of X;
thus ( x >>01<< y implies x,y are_convergent<=1_wrt the reduction of X ) :: thesis: ( x,y are_convergent<=1_wrt the reduction of X implies x >>01<< y )
proof
given z being Element of X such that A1: ( z <=01= x & y =01=> z ) ; :: according to ABSRED_0:def 23 :: thesis: x,y are_convergent<=1_wrt the reduction of X
take z ; :: according to REWRITE1:def 9 :: thesis: ( ( [x,z] in the reduction of X or x = z ) & ( [y,z] in the reduction of X or y = z ) )
( ( x ==> z or z = x ) & ( y ==> z or z = y ) ) by A1;
hence ( ( [x,z] in the reduction of X or x = z ) & ( [y,z] in the reduction of X or y = z ) ) ; :: thesis: verum
end;
set A = the carrier of X;
F0: field the reduction of X c= the carrier of X \/ the carrier of X by RELSET_1:8;
given a being object such that A2: ( ( [x,a] in the reduction of X or x = a ) & ( [y,a] in the reduction of X or y = a ) ) ; :: according to REWRITE1:def 9 :: thesis: x >>01<< y
( a in field the reduction of X or a = x or a = y ) by A2, RELAT_1:15;
then reconsider z = a as Element of X by F0;
take z ; :: according to ABSRED_0:def 23 :: thesis: ( x =01=> z & z <=01= y )
thus ( x = z or x ==> z ) by A2; :: according to ABSRED_0:def 2 :: thesis: z <=01= y
thus ( y = z or y ==> z ) by A2; :: according to ABSRED_0:def 2 :: thesis: verum