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## Homework Statement

Going through a proof of uniqueness for stokes flow for a fluids class I'm taking. Part of it involves replacing the strain tensor (e) with the stress tensor (a), ie going from

(2u)*int(e

_{ij}*e

_{ij})dV

to

int(e

_{ij}*a

_{ij})dV

## Homework Equations

a

_{ij}= -p*d

_{ij}+ 2u*e

_{ij}

d

_{ij}= 1 if i=j, 0 otherwise.

## The Attempt at a Solution

I can see you simply substitute for 2u*e

_{ij}to the integral as follows,

int(e

_{ij}*(e

_{ij}*(p*d

_{ij}+ a

_{ij}))dV

but why does e

_{ij}*p*d

_{ij}= 0 ????????