How to declare array in array in swagger yaml [duplicate]

I would like to declare array in array in swagger, but not sure how to do it: e.g. I have case, with below parameters:

       "cells": [
           [
               {
                   "field": "testID",
                   "name": "testId",
                   "width": "74px",
                   "sortable": true
               },
               {
                   "field": "test number",
                   "name": "test number name",
                   "width": "100px",
                   "sortable": true
               },
               {
                   "field": "testName",
                   "name": "testNamename",
                   "width": "200px",
                   "sortable": true
               },
           ]
       ]
   },

You can see, that JSON parameters are in array, which is in array. I would like to convert this into swagger yaml syntax. I've tried to write something like:

definitions:
  columns:
    type: object
  cells:
    type: array
    items: {
      type: array
      items: {
      properties: 
        field: 
          type: string
        name:
          type: string
        width:
          type: string
        sortable:
          type: boolean
      }
    }

But on the second items I received error message of 'missed comma between the flow collection entries'. Any ideas what it could be?