T. Kobayashi,
A generalized cartan decomposition for the double coset space (U(n1U(n2U(n3))\U(n)/(U(pU(q)), Journal of Mathematical Society of Japan 59 (2007), no. 3, 669-691, math.RT/0607006..
Motivated by recent developments on visible actions on complex manifolds, we raise a question whether or not the multiplication of three subgroups L, G' and H surjects a Lie group G in the setting that G/H carries a complex structure and contains G'/G' ∩ H as a totally real submanifold.

Particularly important cases are when G/L and G/H are generalized flag varieties, and we classify pairs of Levi subgroups (L, H) such that LG'H = G, or equivalently, the real generalized flag variety G'/HG' meets every L-orbit on the complex generalized flag variety G/H in the setting that (G, G') = (U(n), O(n)). For such pairs (L, H), we introduce a herringbone stitch method to find a generalized Cartan decomposition for the double coset space L\G/H, for which there has been no general theory in the non-symmetric case. Our geometric results provides a unified proof of various multiplicity-free theorems in representation theory of general linear groups.

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The original publication is available at projecteuclid.org.

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