How to Safely Convert the Minetown Altar
========================================

There's a very simple and safe way to convert the minetown altar,
and all it takes is an uncursed scroll of earth. The basic idea is to
trap the temple priest between a wall of boulders and one of the temple
walls. This can be easily achieved with a little knowledge of the
priest's movement logic.

There are two basic temple layouts we need to consider. First, let's
consider the simpler case of a temple with a wall only three squares
wide. In the following diagrams, the priest will be marked with an
'H'. This temple layout is from "Grotto Town":

-------
|...H.|
|.._.x|
|..@..|
---+---

Because of a peculiarity in the priest's movement routine (explained in
detail below), the 'x' marks the only space that the priest is allowed
to move to from the illustrated position. Once the priest has moved
there, we read our scroll of earth:

-------
|.....|
|.000H|
|.0@0.|
---+---

Then move north:

-------
|..0H.|
|.0@0x|
|.000.|
---+---

Again, the 'x' marks the only space that the priest is allowed to move
to. We wait in this current position until the priest moves, then move
northwest:

-------
|.@0..|
|.0_0H|
|.000.|
---+---

Again, because of a peculiarity in the priest's AI, he will not be
able to move north from his current position. This allows us to move
the boulder into place and trap him against the wall.

-------
|..@0.|
|.0_0H|
|.000.|
---+---

Here, the minetown altar is yours to convert. The priest will get
angry as usual. But since he can't target you, you're perfectly
safe. If another monster manages to break him free of his prison,
you'll have a fight on your hands.

In larger temples, it will be necessary to trap the priest in the
corner. This layout is from "Frontier Town":

---+--
|....|
|.H0.|
|x0@0|
|.000|
------

In this diagram, we've started as above. However, here the priest
has slightly more freedom to move around. Now is a good time to
explain a bit of the priest's movement logic.

The priest's AI first randomly chooses one of the nine positions on and
around the altar, then moves the priest in the direction that takes him
closest to that target square.

---+--
|....|
|.xxx|
|.x_x|
|.xxx|
------

However, there is one very important restriction on the priest's
movement: he is not allowed to move *into* your line of fire if he is
already *outside of* your line of fire:

---+--
|\.|.|
|H\|/|
|--@-|
|./|\|
------

If he is already inside of your line of fire, then this restriction
doesn't apply and he's allowed to move anywhere. From the foregoing,
we can see that from here:

---+--
|....|
|.H0.|
|x0@0|
|.000|
------

The priest can and will eventually walk onto the square marked with an
'x', which is what we want. If however, we have:

---+--
|\.|.|
|H\0.|
|-0@0|
|.000|
------

We see that the priest is trapped between our lines of fire. It'll be
necessary to move in order to open the way to the 'x'.

Once the priest has stepped onto the desired square, we can move to
trap him in the corner. First by moving northeast:

---+--
|....|
|--0@|
|H0_0|
|.000|
------

We see here that the priest is not allowed to move north or northeast,
allowing us to shove the boulder against the wall:

---+--
|....|
|0@..|
|H0_0|
|x000|
------

Then, once the priest wanders onto the desired spot in the corner, we
trap him:

---+--
|....|
|@...|
|00_0|
|H000|
------

The priest should have about a 2/3 chance of moving out of the corner
immediately after wandering into it. If this happens, you'll get this:

---+--
|@...|
|0...|
|I0_0|
|.000|
------

Which doesn't take a turn, so you'll be able to move southeast to keep
him trapped against the wall. 1/3 of the time, he should stay put in
the corner long enough for you to put the boulder in place.

Don't worry if the priest wanders around a bit. Keep in mind your
lines of fire, and you'll be able to corral him onto the correct
square.