How to wrap an interface in an object while exporting it in TypeScript?

I have a file called x.ts, here is what it holds:

interface x {  x: string;}interface y{  x: string;}interface z {  x: string;}interface i{  x: string;}

I want to export the interfaces like this:

export = {   a: {      x,      y   },   b: {      z,      i   }}

How can I do this in TypeScript?