Typo in Eq.(4)?

[DoranLyong]

Thanks to share your nice work. It gives some inspiration to my study. :)

If you don't mind, I'd like to ask if there's a typo in the formula in Eq. (4).

I think the operator $*$ at the end should be $\cdot$ following the same format in Eq.(3).

[HantingChen]

Sorry for the mistake. We will fix it in the updated version. Thanks!