reserve i,j,n for Nat,
  K for Field,
  a for Element of K,
  M,M1,M2,M3,M4 for Matrix of n,K;
reserve A for Matrix of K;

theorem
  for R being Ring, n being Nat holds ((1.(R,n))@)~ = 1.(R,n)
proof
  let R be Ring; let n;
  (1.(R,n))@=1.(R,n) by Th11;
  hence thesis by Th9;
end;
