superscript and subscript for Greek letters

Dear Users,



I created subscript and superscripts for a Greek letter using  "_"  and " ^
" options. But When i use these with Greek letters output was not good.
Please tell me what needs to be included in my input.

Codes I tried are as follows:

a)   $\displaystyle{\sigma}_{VM}^{2}$ and

b)   $\varepsilon_D$.

Please mention me the correct way to achieve this.

Thanks and regards
Rajaneesh A
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