(P_f_) = PD + P^*D^*.
∴ The vector of the third type represented by (P_f_) is given by the
geometrical sum of the two four-vectors of the first type PD and P^*D^*.
[M. N. S.]
● Transcriber’s Notes:
○ The book's idiosyncratic spelling, emphasis, punctuation, and
symbology especially in mathematical formulas, have been retained.
○ Text that was in italics is enclosed by underscores (_italics_).
Text that was in bold face is enclosed by equals signs (=bold=).
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