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<math xmlns='http://www.w3c.org/mathml' version='2.0'> <apply> <eq/> <apply> <diff/> <bvar> <ci> x </ci> </bvar> <apply> <times/> <ci> a </ci> <ci> u </ci> </apply> </apply> <apply> <times/> <ci> a </ci> <apply> <diff/> <bvar> <ci> x </ci> </bvar> <ci> u </ci> </apply> </apply> </apply> </math>