Hi everybody. I have this function
W = Function[{x, \[Tau]}, \!\(
\*UnderoverscriptBox[\(\[Sum]\), \(n = 1\), \(2\)]\(
\*UnderoverscriptBox[\(\[Sum]\), \(m = 1\), \(2\)]Sin[
\*FractionBox[\(n\ Pi\ x\), \(a\)]] Sin[
\*FractionBox[\(m\ Pi\ y\), \(b\)]]
\*SuperscriptBox[\(E\), \(\(-I\)\
\*SubscriptBox[\(w\), \(n\)] \[Tau]\)]\)\)];
Now I want to write this equation but I don't know how to do that. Please help me. (i attacked the file) 
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