We show that in evolved stars even at relatively low surface ampitude nonradial modes become strongly nonlinear in the hydrogen shell source, where the Brunt-Väisälä frequency has absolute maximum. The measure of nonlinearity is the product of horizontal displacement and radial wavenumber. The value of |H kr| become large already in evolved -Scuti stars. Size of maximum |H kr| become a major problem for nonradial mode hypothesis in RR Lyrae stars.

 
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