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Let $A,B,C,D,E,F$ be vector spaces over a field. Let $x\in A \otimes B \otimes C$ and $y \in D \otimes E \otimes F$ be tensors that are semistable with respect to the natural actions of $\text{SL}(A) ...

In 1976, Luna proved the following important theorem of smooth invariant theory: Let $G$ be a real reductive Lie group and a representation of $G$ on a real finite dimensional vector space $V$. ...

I'm asking this question as a continuation of discussion and answer given by Hugh Thomas at the following post: Why do people study semi-invariant ring (in general)? I have been studying about semi-...