Strongly formal Weierstrass non-integrability for polynomial differential systems in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="double-struck">C</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:math>
Electronic journal of qualitative theory of differential equations