## Can I Ready an attack action to trigger when the target Blinks back to the Material plane?

If my target casts the Blink spell and then Blinks to the Ethereal Plane, can I Ready my action to attack them as soon as they reappear? For example, “shoot them with an arrow when they Blink back to the Material plane?”

I’m wondering about the scenario in which the Villain Blinks and the PCs, who roll good initiative, just stand ready until the Villain blinks back into existence and then they all unleash hell on the Villain at once. It seems to take some of the power out of the spell and I’d like some other perspectives on it.

## Triangle solutions by projection on plane!

I have a little question. how many solutions has a triangle by the projection on the plane? Like the Patenoth problem but in 3d space.

## Can someone break into a Leomund’s Tiny Hut via the Ethereal Plane?

I’ve got players who rely heavily on Leomund’s Tiny hut for a “safe” night time rest. I’m alright with them using it to help, but it gets irritating having a wrench thrown into my nighttime attacks. I have found some ways to deal such as Dispel Magic or having something camp them. One time, I even attacked and killed their horses which were outside the hut. I was going to try a burrowing creature but SageAdvice put forward that there IS a floor in the hut. That’s when I came across the Phase Spider. So the question:

Could something move into the Ethereal Plane, get to an area that would be inside Leomund’s Tiny Hut, and then move back to the Material Plane?

## Classify 2-fold covering spaces of three-times punctured plane

Ahoy Mathematicians,

We are preparing for qualifying exams and ran across this question. There were two proposed methods of approaching it.

1. Recognize that the thrice punctured plane is homotopic to the wedge of 3 circles. Following the example in Hatcher for the 2-fold coverings of the wedge of 2 circles, we construct the 3 connected covering spaces (up to relabeling) of the wedge of three circles. There is also the disconnected covering space of two copies of itself.

2. Use the lifting correspondence to show that the 2 fold covering spaces of the thrice punctured disk are in one-to-one correspondence with subgroups H of $$\mathbb{Z} * \mathbb{Z} * \mathbb{Z}$$ of index 2. There are 3 such groups, giving 3 connected covering spaces.

You’ll notice that the ideas in this agree. The question is one of rigor. Which answer is more accurate? Does Approach 1 actually give us the correct covering spaces, or do we need to think about crossing it with something to cover the surface rather than the 1-mfld? If we use Approach 2, does this answer the question, or do we need to give more of a classification than just the fundamental groups?

Thanks!

## Intersection of a plane and rational cubic curve

Let $$X$$ be a rational cubic curve in $$\mathbb{P}^3$$. Is it true that any hyperplane intersects $$X$$ in exactly $$3$$ points( counted with multiplicity) ?

If it is true, say $$H$$ be a hyperplane intersects $$X$$ at $$x_1, x_2, x_3$$. Consider the line $$l$$ in $$H$$ passing through $$x_1, x_2$$. Then as any line which intersect $$X$$, intersects at $$3$$ points, $$x_3$$ should also lie on $$l$$ or $$l$$ is tangent to $$X$$ at $$x_1$$ or at $$x_2$$. If $$x_3 \in l$$, then the plane $$H_1=: $$, where $$p \in X \setminus l$$ contains at least $$4$$ points of $$X$$, a contradiction. Thus the only possibility is such $$l$$ is always tangent to $$X$$. Thus any line which intersects $$X$$ is always tangent to $$X$$.

## why might a drivers license # be required for a plane trip?

My manager is booking plane tickets for an upcoming conference in another state and he asked me for the following three things:

• my full name as it appears on my drivers license
• my DOB

The first two seem reasonable enough but the last item seems… fishy. I don’t think I’ve ever been asked for a drivers license # when flying. I’ve been asked for a passport # when traveling internationally but not a drivers license #.

I mean, it seems to me that a drivers license shouldn’t even be required for flying. You could be 40yo and not have a drivers license and you could get around exclusively using taxi’s, uber’s and public transit.

I realize a drivers license can be used to verify your identity to TSA but the documents you’re providing to TSA don’t need to be pre-registered or anything…

## Paper – Tetrahedron rolled onto a plane

I am looking for the article Charles W. Trigg, “Tetrahedron rolled onto a plane”, J. Recreational Mathematics, 3(2):82–87, 1970.

It is from @Joseph O’Rourke comment in the previous post “Die-rolling Hamiltonian cycles”

However, I did not see that book anywhere from the Internet. Can anyone please share the information of the book?

Thanks.

## Does the isometry group of a closed simple smooth curve in the plane constrain its perimeter^2/area ratio?

Let $$C$$ be a simple closed smooth curve delimitating a bounded domain $$D$$ in the euclidean plane of isometry group $$G$$ and of given area $$A$$. Does the minimal possible ratio $$\dfrac{P^{2}}{A}$$ where $$P$$ is the perimeter hence the total length of $$C$$ decrease when $$G$$ runs over a sequence $$(G_{i})_{i>0}$$ of groups such that $$i implies $$G_{i}$$ is a strict subgroup of $$G_{j}$$?

## Can Creatures in the Border Ethereal see Invisible creatures on the Material Plane?

As Invisibility and Greater Invisibility are illusion spells and we know that the benefactor of the spell does not actually go anywhere else could they be seen from the Border Ethereal?

Considering See Invisibility allows sight into the Ethereal Plane is it reasonable to assume the other way is also true?

## Would casting banishment on a Revenant permanently send it away to another plane?

In my campaign I’m being chased by a revenant and I’m about to reach level 7. I was thinking of taking banishment to cast on the revenant. The spell states that it brings creatures native to my plane back after a minute but if the creature belongs to another plane it goes there. So because the revenant is dead would it go back to the land of the dead?