as required. Farther, by careful consideration of the branches it can 

 be shown that these P + (s) still have the property 



P + (-s) - P_(s) (10.26) 



enjoyed by the function (10.11) for k + 0. 



Use of these functions enables incompressible problems to be 

 solved much rare elegantly than by taking the limit as k -♦ °° of the 

 more complicated compressible problems, but we should stress that because 

 there is no strip of overlap all procedures should only be regarded as 

 formal, and the results should be verified by independent checks. 



81 



