diff --git a/dlx.py b/dlx.py
--- a/dlx.py
+++ b/dlx.py
@@ -14,7 +14,7 @@ class Cell:
 
 class Column(Cell):
 	def __init__(self,name,*args,**kwargs):
-		super().__init__(*args,**kwargs)
+		super().__init__(*args,up=self,down=self,**kwargs)
 		self.name=name
 		self.size=0
 
@@ -45,10 +45,11 @@ class Column(Cell):
 		self.left.right=self
 
 
-class Header:
-	def __init__(self,left=None,right=None):
-		self.left=left
-		self.right=right
+class Header(Column):
+	def __init__(self):
+		super().__init__("head")
+		self.left=self
+		self.right=self
 		self._res=[]
 
 	def search(self,k=0):
diff --git a/pieces.py b/pieces.py
--- a/pieces.py
+++ b/pieces.py
@@ -72,19 +72,3 @@ def fits(board,piece,shift):
 				if board[coords]: return False
 				res.append(coords)
 	return res
-
-
-if __name__=="__main__":
-	board=np.zeros((1,2,3))
-	boat=np.array([[[0,1,0],[1,1,1]]])
-	es=np.array([[[1,1,0],[0,1,1]]])
-	el=np.array([[[1,1,1],[1,0,0]]])
-
-	pieces={"boat":boat}
-
-	for (name,piece) in pieces.items():
-		for p in listRotations(piece):
-			for shift in listShifts(board,p):
-				fit=fits(board,p,shift)
-				if fit is not False:
-					print(fit)
diff --git a/tetris.py b/tetris.py
--- a/tetris.py
+++ b/tetris.py
@@ -1,122 +1,56 @@
-EMPTY="."
-FULL="O"
-
+import numpy as np
 
-class Piece:
-	def __init__(self,variants):
-		self.variants=variants
+from pieces import listRotations,listShifts,fits
+from dlx import Header,Column,Cell
 
 
-pieceSet=dict()
-
-pieceSet["sq"]=Piece([
-	# OO
-	# OO
-	((0,0),(0,1),(1,0),(1,1))
-])
+board=np.zeros((1,4,3))
+boat=np.array([[[0,1,0],[1,1,1]]])
+sz=np.array([[[1,1,0],[0,1,1]]])
+el=np.array([[[1,1,1],[1,0,0]]])
 
-pieceSet["long"]=Piece([
-	# OOOO
-	((0,0),(0,1),(0,2),(0,3)),
-	((0,0),(1,0),(2,0),(3,0))
-])
-
-pieceSet["boat"]=Piece([
-	# OOO
-	# .O.
-	((0,0),(0,1),(0,2),(1,1)),
-	((0,0),(1,0),(2,0),(1,1)),
-	((0,0),(1,-1),(1,0),(1,1)),
-	((0,0),(1,-1),(1,0),(2,0))
-])
+(nz,ny,nx)=board.shape
+pieces=[("el1",el),("el2",el),("sz",sz)]
+header=[name for (name,p) in pieces]+\
+	[(z,y,x) for z in range(nz) for y in range(ny) for x in range(nx) if not board[z][y][x]]
+index={label:i for (i,label) in enumerate(header)}
 
-pieceSet["sz"]=Piece([
-	# .OO
-	# OO.
-	((0,0),(0,1),(1,-1),(1,0)),
-	((0,0),(1,0),(1,1),(2,1)),
-
-	# OO.
-	# .OO
-	((0,0),(0,1),(1,1),(1,2)),
-	((0,0),(1,0),(1,-1),(2,-1))
-])
+matrix=[]
 
-pieceSet["el"]=Piece([
-	# OOO
-	# O..
-	((0,0),(1,0),(0,1),(0,2)),
-	((0,0),(1,0),(2,0),(2,1)),
-	((0,0),(1,-2),(1,-1),(1,0)),
-	((0,0),(0,1),(1,1),(2,1)),
-
-	# OOO
-	# ..O
-	((0,0),(0,1),(0,2),(1,2)),
-	((0,0),(0,1),(1,0),(2,0)),
-	((0,0),(1,0),(1,1),(1,2)),
-	((0,0),(1,0),(2,0),(2,-1))
-])
-
-WIDTH=8
-HEIGHT=5
-board=[[EMPTY]*WIDTH for r in range(HEIGHT)]
-
+for (name,piece) in pieces:
+	for p in listRotations(piece):
+		for shift in listShifts(board,p):
+			fit=fits(board,p,shift)
+			if fit is not False:
+				row=[0]*len(header)
+				row[index[name]]=1
+				for coords in fit: row[index[coords]]=1
+				matrix.append(row)
 
-def fill(board,pieces):
-	point=firstEmpty(board)
-	if not point: return True
-	res=[]
-	for (i,(k,p)) in enumerate(pieces):
-		if k==0: continue
-		for v in p.variants:
-			if place(board,point,v):
-				pieces[i][0]-=1
-				partialRes=fill(board,pieces)
-				if partialRes:
-					res.append(((point,v), partialRes))
-				remove(board,point,v)
-				pieces[i][0]+=1
-	return res
+# print(header)
+# for row in matrix: print(row)
 
-
-def firstEmpty(board):
-	for (r,row) in enumerate(board):
-		for (c,cell) in enumerate(row):
-			if cell==EMPTY:
-				return (r,c)
-	return None
-
+columns=[]
+head=Header()
+for label in header:
+	c=Column(label)
+	head.left.right=c
+	c.left=head.left
+	head.left=c
+	c.right=head
+	columns.append(c)
 
-def place(board,point,piece):
-	(r,c)=point
-	if not all(0<=r+ri<HEIGHT and 0<=c+ci<WIDTH and board[r+ri][c+ci]==EMPTY for (ri,ci) in piece):
-		return False
-	for (ri,ci) in piece:
-		board[r+ri][c+ci]=FULL
-	return True
-
-
-def remove(board,point,piece):
-	(r,c)=point
-	for (ri,ci) in piece:
-		board[r+ri][c+ci]=EMPTY
-
+for row in matrix:
+	cells=[]
+	for (item,col) in zip(row,columns):
+		if item!=1: continue
+		c=Cell(up=col.up,down=col,col=col)
+		col.up.down=c
+		col.up=c
+		cells.append(c)
+		c.right=cells[0]
+		c.left=cells[0].left
+		c.left.right=c
+		c.right.left=c
 
-def visualise(board,tree,letter="A"):
-	if tree is True:
-		for row in board:
-			print("".join(row))
-		print()
-		return
-	for (((r,c),piece),rest) in tree:
-		for (ri,ci) in piece:
-			board[r+ri][c+ci]=letter
-		visualise(board,rest,chr(ord(letter)+1))
-
-
-res=fill(board,[[k,pieceSet[x]] for (k,x) in [(2,"sq"),(2,"el"),(2,"boat"),(2,"long"),(2,"sz")]])
-if res:
-	visualise(board,res)
-else:
-	print(res)
+head.search()