deletions | additions       diff --git a/section_Constitutive_relationships_Retardation_factor__.tex b/section_Constitutive_relationships_Retardation_factor__.tex  index 95f62e8..e56458f 100644  --- a/section_Constitutive_relationships_Retardation_factor__.tex  +++ b/section_Constitutive_relationships_Retardation_factor__.tex 
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Mass conservation law.  \begin{align}  \frac{\partial u}{\partial t} = -\frac{v}{R(C)}  \nabla {C} \cdot \left( v u \right)  + \nabla \cdot \left( D \nable u \right)  \\ \end{align}  Darcy law.