# Sokoban Level 4b
Sokoban Level 4a is one of two possible maps for the last level of Sokoban in NetHack, and is among the various possible maps for that level in variants of NetHack. Behind the holes is a treasure zoo with three doors - inside one of the doors is the branch prize, which has an equal chance of being a bag of holding or an amulet of reflection. There are 20 boulders and 18 holes, leaving two spare boulders.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Both prizes are no longer equally likely for each floor. Instead, floor 4a has a 75% chance for a bag of holding, and this floor has a 75% chance for an amulet of reflection.
0 boulder
^ hole
@ starting position/downstairs
  no upstairs

  ------------------------
  |..^^^^^^^^^^^^^^^^^^..|
  |..-------------------.|
----.|    -----        |.|
|..|0--  --...|        |.|
|.....|--|.0..|        |.|
|.00..|..|..0.|        |.|
--..00|...00.--        |.|
 |0..0...|0..|   ------|.|
 |.00.|..|..0| --|.....|.|
 |.0.0---|.0.| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.0..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.0...|   |.+.....|
     |@.|..|   --|.....|
     -------     -------

Contents

1 Strategy
2 History
3 Variants

3.1 UnNetHack
3.2 EvilHack
3.3 Hack'EM

Strategy
The following solution solves the level without putting any boulders in an immobile position. Faster solutions which do not necessarily leave every boulder free might exist.
All boulders are replaced by letters so they can be referred to. Moving the boulders is shortened to r for right, l for left, u for up, d for down. An asterisk is used to denote the last move filled a hole (and thus removed the boulder from the game). So Nddrr* means move boulder N two times down and two times to the right into a hole.
The general strategy for this level is to enter through the right room into the middle of the left room. There the boulders should be organized precisely so that the left room can be cleared.
You can also watch an instructional TTYREC video or a YouTube video.
At first the T boulder should be pushed into the right room, because the entrance above the T should stay clear:

  ------------------------ T rrru uuu
  |..^^^^^^^^^^^^^^^^^^..| R u
  |..-------------------.| O uu
----.|    -----        |.| I u
|..|A--  --...|        |.| H lll
|.....|--|.B..|        |.|
|.CD..|..|..E.|        |.|
--..FG|...HI.--        |.|
 |J..K...|L..|   ------|.|
 |.MN.|..|..O| --|.....|.|
 |.P.Q---|.R.| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.T...|   |.+.....|
     |@.|..|   --|.....|
     -------     -------

In the left room align the boulders to form a 2x3 area in which you are able to turn boulders around. These moves are the most crucial to successfully finishing this level:

  ------------------------ K ll
  |..^^^^^^^^^^^^^^^^^^..| N d
  |..-------------------.| F u
----.|    -----        |.| G u
|..|A--  --...|        |.|
|.....|--|.B..|        |.|
|.CD..|..|.IE.|        |.|
--..FG|H@...O--        |.|
 |J..K...|L..|   ------|.|
 |.MN.|..|.R.| --|.....|.|
 |.P.Q---|T..| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.....|   |.+.....|
     |&gt;.|..|   --|.....|
     -------     -------

Finish boulder A by moving C around. Then finish F through the 2x3 area and clear C and D:

  ------------------------ C ud
  |..^^^^^^^^^^^^^^^^^^..| A uuur*
  |..-------------------.| F dduu uuuu urr*
----.|    -----        |.| C u
|..|A--  --...|        |.| D ruuu uurr r*
|.....|--|.B..|        |.| C rruu uurr rr* 
|.CDFG|..|.IE.|        |.|
--....|H....O--        |.|
 |JK@....|L..|   ------|.|
 |.M..|..|.R.| --|.....|.|
 |.PNQ---|T..| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.....|   |.+.....|
     |&gt;.|..|   --|.....|
     -------     -------

Clear the rest of the left room:

  ------------------------ N uuuu uuuu urrr rr*
  |....@.^^^^^^^^^^^^^^..| P ruuu uuuu uurr rrrr*
  |..-------------------.| M ruuu uuuu urrr rrrr*
----.|    -----        |.| K uuur uuuu rrrr rrrr*
|..|.--  --...|        |.| J uuur ruuu urrr rrrr rr*
|.....|--|.B..|        |.|
|....G|..|.IE.|        |.|
--....|H....O--        |.|
 |JK.....|L..|   ------|.|
 |.M..|..|.R.| --|.....|.|
 |.PNQ---|T..| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.....|   |.+.....|
     |&gt;.|..|   --|.....|
     -------     -------

Now it is possible to either clear the remaining boulders in the left room, or continue with the middle and right room. Note that to move T we must pass to the north opening of the small room with the stairs:

  ------------------------ H dlll uuuu uuur rrrr rrrr r*
  |.........@.^^^^^^^^^..| R d
  |..-------------------.| L ulll dlll uuuu uuur rrrr rrrr rr*
----.|    -----        |.| T uuul lldl lluu uuuu urrr rrrr rrrr r*
|..|.--  --...|        |.| R luuu llld lllu uuuu uurr rrrr rrrr rrr*
|.....|--|.B..|        |.| B r
|....G|..|.IE.|        |.| I dddl uull ldll luuu uuuu rrrr rrrr rrrr rr*
--....|H....O--        |.| E lldl lldl lluu uuuu urrr rrrr rrrr rrrr*
 |.......|L..|   ------|.| B dlld llld lllu uuuu uurr rrrr rrrr rrrr rr*
 |....|..|.R.| --|.....|.| G ddlu uuuu uurr rrrr rrrr rrrr rrr*
 |...Q---|T..| |.+.....|.| Q uulu uuuu uurr rrrr rrrr rrrr rrrr*
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+.|
    ---.--.|   |-|.....|--
     |.....|   |.+.....|
     |&gt;.|..|   --|.....|
     -------     -------

In the large room behind the door is a treasure zoo. Behind one of the three doors in the zoo is a square with the prize item atop a burnt "Elbereth" and a cursed scroll of scare monster. Also remember to check under boulder S for usable items.

  ------------------------
  |......................|
  |..-------------------.|
----.|    -----        |.|
|..|.--  --...|        |.|
|.....|--|....|        |.|
|.....|..|....|        |.|
--....|.....O--        |.|
 |.......|...|   ------|.|
 |....|..|...| --|.....|.|
 |....---|...| |.+.....|.|
 |.......|..-- |-|.....|.|
 ----.S..|.--  |.+.....+@|
    ---.--.|   |-|.....|--
     |.....|   |.+.....|
     |&gt;.|..|   --|.....|
     -------     -------

History
In NetHack 3.4.3 and earlier versions, including some variants based on these versions, the prize is always an amulet of reflection, with no cursed scroll of scare monster underneath it. As of NetHack 3.6.0, the cursed scroll of scare monster is added, and there is a 50% chance for the prize to be either a bag of holding or an amulet of reflection.

Variants
UnNetHack
In UnNetHack, this level may be flipped horizontally or vertically like all Sokoban levels. The prize is also changed to a choice from one of the following: a bag of holding, a cloak (of magic resistance or displacement) and an amulet (of reflection, life saving or ESP).

EvilHack
In EvilHack, the choice is between a prize tool (a bag of holding or a magic marker), a prize armor (a helm of speed or a pair of gauntlets of protection), or a prize amulet (an amulet of reflection or magic resistance). As soon as one of the doors is opened, the others will seal: some form of object detection is recommended if you are aiming for a specific reward.

Hack'EM
In Hack'EM, this level is named "Reflectoban". Like EvilHack, the choice is between a prize tool (a bag of holding or a magic marker), a prize armor (a helm of speed or a pair of gauntlets of protection), or a prize amulet (an amulet of reflection or magic resistance). As soon as one of the doors is opened, the others will seal: as in EvilHack, a form of detecting the prizes is recommended if you are aiming for a specific reward.