docs: function countVertices(cells) {
    var vc = -1
      , max = Math.max
    for(var i=0, il=cells.length; i<il; ++i) {
      var c = cells[i]
      for(var j=0, jl=c.length; j<jl; ++j) {
        vc = max(vc, c[j])
      }
    }
    return vc+1
  }