User:Nic bor

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${\frac {\partial \mathbf {u} }{\partial t}}+{\mathbf {v} }\cdot \nabla \mathbf {u} +\mathbf {u} *\nabla \cdot {\mathbf {v} }=d\nabla ^{2}\mathbf {u}$

${\frac {\partial \mathbf {u} }{\partial t}}+{\mathbf {v} }\cdot \nabla \mathbf {u} =0$

${\frac {D\mathbf {u} }{Dt}}\equiv {\frac {\partial \mathbf {u} }{\partial t}}+{\mathbf {v} }\cdot \nabla \mathbf {u}$

${\frac {D\mathbf {u} }{Dt}}=0$