# What does the term 'a uniform RVB spin-liquid state' mean?

I encountered this term a uniform RVB spin-liquid state in some articles, for example, see the paragraph under Eq.(29) on page 9 in this paper.

What does the word 'uniform ' mean? Simply from the mean-field anzats(see Eq.(28)), how to see that the projected spin wave-function is a RVB state which is a superposition of spin-singlet states? And is the low-energy gauge structure of a uniform RVB spin-liquid state always $SU(2)$?

Thank you very much.

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