ELI5: Explain Like I'm 5

Reflexive subspace lattice

Okay kiddo, let's talk about reflexive subspace lattices in a way that's easy to understand.

Imagine you have a big block of Legos. Each Lego can represent a subspace. Subspaces are sets of vectors that are closed under addition and scalar multiplication. Think of them like building blocks for bigger spaces.

Now, let's say you take some of these Legos and stack them on top of each other to create a tower. This tower represents what's called a lattice. A lattice is just a bunch of subspaces that are ordered in a particular way, like building blocks stacked on top of each other.

But what if you want to look at a smaller part of the lattice? Maybe you just want to look at a certain group of Legos that are all connected to each other, like a mini-subset of the bigger tower. That's what a reflexive subspace lattice is. It's just a smaller collection of subspaces that have a certain relationship to each other.

The relationship they have is a bit tricky to explain, but it's basically like this. Imagine you have a mirror that shows you a reflection of the lattice. If the reflection looks the same as the original lattice, then it's said to be reflexive. It's kind of like a mirror image, but instead of a picture of yourself, it's a picture of the lattice.

So to sum it up, a reflexive subspace lattice is a smaller collection of subspaces that have a special relationship to each other. This relationship is like a mirror image of the original lattice. It's like picking out certain Legos from a big pile and stacking them in a way that looks the same when you hold up a mirror.