I should probably clarify this; the goal here is to promote Medium writers' work on Medium. If there is an external link - and provided it is not an affiliate link or a link to porn, but rather to something that supports a point - it's not an automatic NO. There's a LITTLE wiggle room, here, but we would strongly PREFER it if you don't drive us off-site often, if at all.

Same goes for the FOUR other authors. If you slip in a fifth, it's a lopsided geometric shape and no longer a rhombus, but...meh. If it's good, related, and you just can't help promoting FIVE other writers instead of FOUR, well...we'll probably send you back to Geometry class, but it's not an automatic NO.