Bifurcation of limit cycles from a 4-dimensional center in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msup><mml:mi mathvariant="double-struck">R</mml:mi><mml:mi>m</mml:mi></mml:msup></mml:math> in resonance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:mn>1</mml:mn><mml:mo>:</mml:mo><mml:mi>N</mml:mi></mml:math>
Journal of mathematical analysis and applications