Kravchenko, V. V. <br/><br/>
Helmholtz operator with a quaternionic wave number and asso-ciated function theory / by V. V. Kravchenko and M. V. Shap-iro. 

 - México, D. F. : tamento de Matemáticas 
 - 35 p. 
 - Reporte interno; no. 96 / Instituto Politécnico Nacional, C-INVESTAV, Departamento de Matemáticas .