The first statement of a row within a piece is called the prime form (P) of the row. Notice what happens to a row’s intervals when the row is transformed by inversion (I), retrograde (R), and retrograde inversion (RI):
I flipped same
R flipped reverse
RI same reverse
A row’s intervallic pattern can be built starting on any pitch class (pc). We identify that pc using a subscript: P5 is the prime form of the row starting on pc 5. The note on which the row is built, the referential pitch class, moves to the end for both the R and RI forms of the row! Use the last note’s pitch class number as the subscript for R and RI forms of the row.