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
  1_Rmatrix(0)=0_Rmatrix(0) & 1_Rmatrix(0)={}
proof
A1: len 1_Rmatrix(0) = 0 by MATRIX_0:24;
  len 0_Rmatrix(0) = 0 by MATRIX_0:24;
  then 0_Rmatrix(0)={};
  hence 1_Rmatrix(0)=0_Rmatrix(0) by A1;
  thus thesis by A1;
end;
