First-time and second-time seen edges in DFS on undirected graphs

Assume an undirected graph and a DFS traversal on it. I am interested in the DFS tree which encodes the discoverer/discovered (parent/child) relationships of the traversal. Just to make sure we are on the same page, define a discovered vertex x as one that has been visited but descendants of it are still being processed, i.e., we have not yet returned back to x. Define, a processed vertex x as one that we have returned to after we have recursed into all of its descendants and we mark it as such upon return.

Let us define the following edge types on that tree

  • Tree edges: direct parent/child edges: the parent is the one to first discover the child.
  • Back edges: edge from a descendant to an ancestor at least 2 levels up on the tree: the descendant sees an already discovered vertex.

Those are the only two types of edges one can have on undirected graph DFS. Now, I have been reading The Algorithm Design Manual (page 173) which discusses the following:

  • Given an undirected graph DFS and an edge (x,y) as seen from x how can we tell whether we have seen this edge before from the side of y?

I can understand the cases when y is undiscovered or discovered but not yet processed.

However, the book says that if y is processed then we can say that it’s the 2nd time (i.e., we have seen the edge (x,y) from y before); this is because we should have seen all edges coming out of y before marking it as processed. The part I don’t understand is when such a case can occur. How can we see y again after we have marked it processed? Can you give me an example of such a graph?

Is there any more information about the mines seen on the map of Chult in Tomb of Annihilation?

In Tomb of Annihilation, in chapter 2, there is a map of Chult on p. 39, the “DM’s version” with all of the hexes filled in and all of the locations named and displayed.

However, although many of the locations are named, there are various “mines” that are shown throughout the map (and we can tell that they are mines because the legend tells us that that’s what that symbol means), but unlike the named locations, they are not expanded on later in chapter 2.

Below is a section of the map showing a few of these mines (shown by the symbol of a spade and pickaxe), as well as a few examples of named locations (in spoiler quotes in case any players currently in a ToA game shouldn’t be looking at it):

What is the purpose of these mines being on the map? If my players find one, what am I supposed to do with that? Is there any further information on these mines in the book? Hopefully I’m just being blind and it’s right there under my nose, but I can’t seem to find anything else about these mines…

Daggerspell guardians – anyone ever seen or created stats for “The emerald knives of seven truths” (3.5)

In the ‘Complete Adventurer’ the Daggerspell Guardians are seeking a pair of daggers called the emerald knives of seven truths.

“Lore of the Guild: Many of the greatest treasures of the Daggerspell Guardians are daggers of great power. Two of the most treasured of these daggers, the emerald knives of seven truths, were lost years ago by a daggerspell shaper who fell in battle against a powerful vampire named Malkan Ry-Ul. Both the knives and the vampire have been missing for many years, but recently travelers from the east have reported that a great city there is haunted by a killer who leaves strange green cuts on the bodies of his victims – a signature side effect of the magic of the emerald knives”.

Has anyone seen or created (or have any advice) for their stats please?

For info: I’m playing a daggerspell shaper searching for them.

To qualify to become one a character must fulfill all the following criteria:

Alignment: Any nonevil.
Skills: Concentration 8 ranks.
Feats: Weapon Focus (dagger), Two-Weapon Fighting.
Special: Wild shape class feature.
Special: Either sneak attack +1d6 or skirmish +1d6.

This makes me wonder if the daggers either do some of these things (as they may have inspired the creation of said group in the first place)?!

How can I replicate an aura of power as seen in anime?

In anime (and manga) there are often characters who exude an aura of power. Is there anything in the D&D 5th edition ruleset that would duplicate this effect?

The aura doesn’t necessarily need to do anything mechanically. The only requirement is that it must be visible under normal conditions (e.g. you don’t need to have darkvision, be under moonlight, have a special class ability or feat to see it).

If the aura can increase a character’s power, so much the better.

Must I have seen a Flower with my own eyes to use Staff Of Flowers?

I’ve said this before but The Staff Of Flowers from Xgte is a surprisingly useful item for it’s level.

But what I want to know is does the staff require me to know a flower, or just know of a flower? Specifically I want to know exactly how much knowledge of a flower is reasonable to grow it. Does one need to know the name? How it looks? Where it grows? How it can be used? All of the above?

Does one even need to know it’s a flower to make it grow? If a character has never seen Sugar Cane and hears the name and they want to know if it’s a flower or not, can they grow it? What if they know everything else about the plant except that it’s a flower and they want to confirm it?

Why exactly is programming, and programming only, seen as a worthless skill that “anyone can learn”?

You never hear anyone claim that everyone can or should be bridge engineers, or deal with air planes, or stuff related to space, or surgery, or any other critical and highly complex profession/task.

Yet there isn’t one day without what passes for “tech news” these days pushing another “AI code generation” tool or “coding boot camp”. Programming is apparently seen as mindless mashing of keys on a keyboard, instead of the highly complicated engineering task that it is, where 99.99% of the work is in your brain and only the last 0.01% is actually typing in code.

I must say that, unlike for most things, I don’t even have a controversial explanation to this. The “ones in power” want to dumb the masses down, so aggressively having them do programming makes zero sense. If their goal is to kill the entire concept of programming, they are well on their way, with most websites and any kind of software already being so broken that one might as well start over from scratch at this point, with entirely new computers, operating systems and software…

It doesn’t make any sense to me that they are trying to push this. They cannot themselves be stupid enough to believe that the average person is ever going to program anything of any value, just like Joe Sixpack will never perform critical brain surgery or come up with the algorithms for the manned Mars mission.

So why have the masses believe that programming is like sitting at a counter? What possible benefit could come from this? Even rich people, to the best of my knowledge, still have to use the same OSes and (to a large extent) software. Surely they don’t want what they are using to be insecure, broken garbage? Or do “the 1%” have entirely dedicated hardware and software?

If I used Wish to become immune to being seen via Truesight and stand in an area of magical darkness, can a creature with Truesight see me?

As the title says, does standing inside an area of magical darkness, while being immune from detection through truesight (not the spell, but the monster ability), render me unseen from a creature that has truesight?

On the one hand, the answer might be yes. I am undetectable by truesight now, and truesight is what is enabling the creature to see me.

On the other hand, the answer might be no. Truesight allows the creature to see through the magical darkness and I am not actually invisible.

Which is the answer that has more adherence to the rules as written? Or is this a gray area in the rules?

What are some unusual or creative implementations of ADTs you’ve seen?

While learning about ADTs in a data structures course, we learned that the List ADT is most commonly implemented using linked nodes or arrays. Are there any other fundamentally different and unusual implementations of the List ADT or any others that are ever used in practice or even ones that might satisfy all of the properties? If so, what are some benefits and drawbacks of these?