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where a(x, y, ξ) is a symbol of order k. This purine bases Purine and its substitu-
defines a bounded linear operator between the tion derivatives, especially naturally occurring
s
Sobolev spaces P : H (M) → H s−k (M). examples.
c c
psychometry The use of a wet-and-dry bulb pyrimidine bases Pyrimidine and its substi-
thermometer for measurement of atmospheric tution derivatives, especially naturally occurring
humidity. examples.
© 2003 by CRC Press LLC
