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Sep 16, 2015 at 20:39 history edited Aaron Tikuisis CC BY-SA 3.0
Changed = to := for consistency.
Sep 16, 2015 at 20:39 comment added Aaron Tikuisis Alessandro: adding that hypothesis doesn't help. Let $U$ be the projection onto $e_1$ and $V$ the projection onto $e_2$ (so that $U,V$ are orthogonal to $S_i,T_i$ for $i>2$), and then define $S_i' := U + \epsilon S_i$ and $T_i':= V + \epsilon T_i$.
Sep 16, 2015 at 17:19 vote accept Alessandro Vignati
Sep 16, 2015 at 17:19 comment added Alessandro Vignati Uhg.You're right. And if I need them to be positive I can just take the projections onto $e_0+e_i$ and $e_0-e_i$. So even if $A$ is $\mathbb C^2$ that wouldn't work (answering Yemon). Thanks! Naively, what if there are operators $U$ an $V$, and $\epsilon>0$ (small enough) such that for all $i$ we have $||S_i-U||, ||T_i-V||<\epsilon$ (and everything has norm $1$!)
Sep 16, 2015 at 16:22 comment added Yemon Choi Naive question: for which $A$ would Alessandro's question have a positive answer? (There is something in the original question which reminds me of AMNM, although it isn't actually the same)
Sep 16, 2015 at 14:08 history answered Aaron Tikuisis CC BY-SA 3.0