   f(x) for x in ar
 
 dup = (obj) ->
+  return null unless obj?
   if ( obj instanceof Array )
     map obj, (o) -> dup o
   else if ( typeof obj == 'object' )

  margins: ->
    m = @marges ?= []
    return m if m.length
    fi = PI * @visualAngle() / 2
    t1 = @angle - fi
    t1 = @universe.tp( sin(t1), cos(t1) )
    t2 = @angle + fi

    @type      = Thing
    @others    = {}
    @outlined  = false
    @marges    = null
    unless @dontAdd
      uni = @universe
      uni.change = true
