Similarities of subspace lattices in Banach spacesBračič, Janko (Avtor) Kandić, Marko (Avtor) subspace latticecollineationnormalizerreflexive latticeVolterra nestA collineation of a subspace lattice ${\mathfrak L}$ in a complex Banach space ${\mathscr X}$ is an invertible operator $S$ on ${\mathscr X}$ with the property that the image $S{\mathscr M}$ of a subspace ${\mathscr M}$ belongs to ${\mathfrak L}$ if and and only if ${\mathscr M}$ belongs to it. Hence, $S$ is a collineation of ${\mathfrak L}$ if and only if it implements an order automorphism of ${\mathfrak L}$. We study the group ${\rm Col}({\mathfrak L})$ of all collineations of ${\mathfrak L}$ and its subgroup ${\rm Grp}({\rm Alg}({\mathfrak L}))$ of all invertible operators that fix every subspace in ${\mathfrak L}$. We show that ${\rm Grp}({\rm Alg}({\mathfrak L}))$ is a normal subgroup of ${\rm Col}({\mathfrak L})$; moreover, if ${\mathfrak L}$ is a reflexive subspace lattice, then ${\rm Col}({\mathfrak L})$ is the normalizer of ${\rm Grp}({\rm Alg}({\mathfrak L}))$ in the group of all invertible operators on ${\mathscr X}$. One of the main questions that we consider is whether ${\rm Grp}({\rm Alg}({\mathfrak L}))$ is a complemented subgroup in ${\rm Col}({\mathfrak L})$. For certain subspace lattices ${\mathfrak L}$, such as some realizations of the diamond or the double triangle, some nests in the space of continuous functions on $[0,1]$, and the classical Volterra nest in $L^1[0,1]$, we characterize the complement of ${\rm Grp}({\rm Alg}({\mathfrak L}))$ in ${\rm Col}({\mathfrak L})$. On the other hand, for the Volterra nests in $L^p[0,1]$, where $1<p<\infty$, a further study is needed, and we prove only some partial results.20262026-06-08 12:08:05Neznano29841sl