Question: calculate sum w2(x,y)

I need to calculate sum w2(x,y),

v2 := proc (x, y) options operator, arrow; sin(x)*cos(y) end proc;
u2 := proc (x, y) options operator, arrow; 3*sin(x)-cos(y) end proc;
w2 := proc (x, y) options operator, arrow; diff(v2(x, y), x)-(diff(u2(x, y), y)) end proc;
L1 := proc (x, y) option inline; abs(w2(x, y)) end proc; CodeTools:-Usage(evalhf(add(add(abs(w2(x, y)), x = 0 .. 10), y = 0 .. 10)));
Error, (in CodeTools:-Usage) unable to evaluate built-in function `diff` in evalhf

 but it is error , how  can be rewritten properly?

 

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