reserve p,q,r,th,th1 for Real;
reserve n for Nat;

theorem Th12:
  exp_R.(p+q) = exp_R.(p) * exp_R.(q)
proof
  exp_R.(p+q) = exp_R(p+q) by SIN_COS:def 23
    .= exp_R(p) * exp_R(q) by SIN_COS:50
    .= exp_R.(p) * exp_R(q) by SIN_COS:def 23
    .= exp_R.(p) * exp_R.(q) by SIN_COS:def 23;
  hence thesis;
end;
