Groen, P. P. N. De. <br/><br/>
Singularly perturbed differential operators of second order   

 - Amsterdam  Mathematisch Centrum  1976 
 - ix, 159p. Ref. 
 - Mathematical centre tracts   v. 68 .
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<br/><br/><label>Dewey Class. No.: </label>515.35  / G874.SP