reserve x for set,
  D for non empty set,
  k,n,m,i,j,l for Nat,
  K for Field;
reserve n,i,j for Nat;
reserve n for Nat;

theorem Th88:
  for x being FinSequence of REAL st len x=n holds x*(1_Rmatrix n) =x
proof
  let x be FinSequence of REAL;
A1: width (LineVec2Mx x)=len x by MATRIXR1:def 10;
  assume len x=n;
  then x*(1_Rmatrix n) =Line(MXF2MXR (MXR2MXF (LineVec2Mx x)),1) by A1,Th67
    .=x by MATRIXR1:48;
  hence thesis;
end;
