deletions | additions       diff --git a/section_Constitutive_relationships_Retardation_factor__.tex b/section_Constitutive_relationships_Retardation_factor__.tex  index 8121e05..09730cf 100644  --- a/section_Constitutive_relationships_Retardation_factor__.tex  +++ b/section_Constitutive_relationships_Retardation_factor__.tex 
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\frac{\partial S}{\partial u} = b k_p u^{b-1}  \end{align}  \subsection{Fluid velocity:} velocity field:}  \begin{align}  v = \frac{v_e}{R(u)}  \end{align} 
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D = \frac{D_l}{R(u)}  \end{align}  Constants: $b$, $k_p$,$v_e$,  $D_l$ Velocity field: $v_e$  \section{Partial differential equation}