diff --git a/dlx.py b/dlx.py
--- a/dlx.py
+++ b/dlx.py
@@ -4,17 +4,30 @@
 
 
 class Cell:
-	def __init__(self,left=None,right=None,up=None,down=None,col=None):
-		self.left=left
-		self.right=right
-		self.up=up
-		self.down=down
+	def __init__(self,col):
+		self.left=self
+		self.right=self
+		self.up=self
+		self.down=self
 		self.col=col
 
+	def attachRight(self,c):
+		"""...-(b)-(self)->  <-(c)-(d)-..."""
+		self.right.left=c.left
+		c.left.right=self.right
+		self.right=c
+		c.left=self
+
+	def attachDown(self,c):
+		self.down.up=c.up
+		c.up.down=self.down
+		self.down=c
+		c.up=self
+
 
 class Column(Cell):
-	def __init__(self,name,*args,**kwargs):
-		super().__init__(*args,up=self,down=self,**kwargs)
+	def __init__(self,name):
+		super().__init__(self)
 		self.name=name
 		self.size=0
 
@@ -48,8 +61,7 @@ class Column(Cell):
 class Header(Column):
 	def __init__(self):
 		super().__init__("head")
-		self.left=self
-		self.right=self
+		self.up=self.down=self.size=None
 		self._res=[]
 
 	def search(self,k=0):
@@ -63,17 +75,17 @@ class Header(Column):
 		col.cover()
 		row=col.down
 		while row is not col:
-			row=row.down
 			self._res[k]=row
 			c=row.right
 			while c is not row:
 				c.col.cover()
-				self.search(k+1)
-				c=row.right
+				c=c.right
+			self.search(k+1)
 			c=row.left
 			while c is not row:
 				c.col.uncover()
 				c=c.left
+			row=row.down
 		col.uncover()
 
 	def chooseCol(self):
@@ -89,6 +101,7 @@ class Header(Column):
 
 	def print(self):
 		for r in self._res:
+			print(r.col.name,end=" ")
 			c=r.right
 			while c is not r:
 				print(c.col.name,end=" ")
diff --git a/tetris.py b/tetris.py
--- a/tetris.py
+++ b/tetris.py
@@ -27,30 +27,25 @@ for (name,piece) in pieces:
 				for coords in fit: row[index[coords]]=1
 				matrix.append(row)
 
-# print(header)
-# for row in matrix: print(row)
+print(header)
+for row in matrix: print(row)
 
 columns=[]
 head=Header()
 for label in header:
 	c=Column(label)
-	head.left.right=c
-	c.left=head.left
-	head.left=c
-	c.right=head
+	c.attachRight(head)
 	columns.append(c)
 
 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
+		c=Cell(col)
+		c.attachDown(col)
 		cells.append(c)
-		c.right=cells[0]
-		c.left=cells[0].left
-		c.left.right=c
-		c.right.left=c
+		c.attachRight(cells[0])
+		col.size+=1
 
+print()
 head.search()