theorem Th92:
  |.0c n.| = 0
proof
  thus |.0c n .| = sqrt Sum sqr (n |-> (0 qua Real)) by Th89
    .= sqrt Sum (n |-> (0 qua Real)^2) by RVSUM_1:56
    .= sqrt (n*(0 qua Nat)) by RVSUM_1:80
    .= 0;
end;
