Question: why maple can't solve this integral?

Hi, I try to solve the below integral. when I press enter key maple dosen't show answer and show the integral again.

int(r*r[bc]*r[tc], r = r[bc] .. r[tc]);

but when I write intgral this way and use " i " as subscript ,maple solve it.

int(r[i]*r[bc]*r[tc], r[i] = r[bc] .. r[tc]);

I just want to know why?

what is difference between first and second integral?

and also is there any way (or any packages) to solve these integrals?

(I read https://www.maplesoft.com/applications/view.aspx?SID=6846&view=html article befor)

thanks.

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