I read some tutorial papers and slide，and find that the bases on Reproducing Kernel Hilbert Spaces always be orthonormal. For examples，you can refer to this link for the content about Reproducing Kernel Hilbert Spaces. What if the introduced base are not orthonormal? Any papers talk about this problems?

`e_m`

in Eq.(1) mentioned in the link. Then, if the kernel still has the original property like:`𝑓(𝑎)=⟨𝑓,𝐾𝑎⟩`

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