Question about diffusion rate β_t

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1) Any idea on the highlighted sentence in lilianweng blog which illustrates the μ_bar(x_t, x_0) expression ?

2) The highlighted sentence in DDPM paper does not make sense to me.

3) I also tried checking the reference [53] , but it seems different in that reference though.

4) What is the actual purpose of "clipping" mentioned in #5 ?

[buttercutter]

@lilianweng could you help with the above ?