Some theorists use angle brackets to denote ordered sequences , while others distinguish ordered sets by separating the numbers with spaces . Thus one might notate the unordered set of pitch classes 0, 1, and 2 (corresponding in this case to C, C, and D) as {0,1,2}. The ordered sequence C-C-D would be notated or (0,1,2). Although C is considered zero in this example, this is not always the case. For example, a piece (whether tonal or atonal) with a clear pitch center of F might be most usefully analyzed with F set to zero (in which case {0,1,2} would represent F, F and G. (For the use of numbers to represent notes, see pitch class.)