theorem
  [.a,b |^ i.] = (b |^ a) |^ (- i) * (b |^ i)
proof
  thus [.a,b |^ i.] = (b |^ (- i)) |^ a * (b |^ i) by GROUP_1:36
    .= (b |^ a) |^ (- i) * (b |^ i) by GROUP_3:28;
end;
