diff --git a/src/command_prompt.py b/src/command_prompt.py
index 54712a5..70e012b 100644
--- a/src/command_prompt.py
+++ b/src/command_prompt.py
@@ -20,7 +20,7 @@ import os.path
 
 import filecheck
 import colors
-from polyomino import Cross,Disk
+from polyomino import Cross,Disk,Staircase
 
 class Command_prompt(Label):
     
@@ -388,6 +388,8 @@ class Command_prompt(Label):
             self.app.painter.shape=Cross
         elif argv[2]=="disk":
             self.app.painter.shape=Disk
+        elif argv[2]=="staircase":
+            self.app.painter.shape=Staircase
         else:
             self.message="error: unrecognized shape '"+argv[2]+"'; supported shapes are cross|disk"
             return
diff --git a/src/painter.py b/src/painter.py
index cae39cb..cef8b4c 100644
--- a/src/painter.py
+++ b/src/painter.py
@@ -21,7 +21,7 @@ from kivy.core.window import Window
 from kivy.graphics import Color,Line,Rectangle
 
 from point import Point
-from polyomino import Cross,Disk
+from polyomino import Cross,Disk,Staircase
 
 from tools import remove_fromlist
 
@@ -536,8 +536,12 @@ class Painter(Widget):
         # save state (particle shape, zoom, lattice)
         if self.shape==Cross:
             ff.write("%shape=cross\n")
-        else:
+        elif self.shape==Disk:
             ff.write("%shape=disk\n")
+        elif self.shape==Staircase:
+            ff.write("%shape=staircase\n")
+        else:
+            print("bug: unrecognized shape in write: '"+str(self.shape)+"'")
         ff.write("%zoom={:1.1f}\n".format(self.base_size/50))
         ff.write("%color={:d},{:d},{:d}\n".format(self.color[0],self.color[1],self.color[2]))
         if self.lattice != None:
@@ -547,6 +551,8 @@ class Painter(Widget):
                 ff.write("{:d};".format(CROSS_INDEX))
             elif type(particle)==Disk:
                 ff.write("{:d};".format(DISK_INDEX))
+            elif type(particle)==Staircase:
+                ff.write("{:d};".format(STAIRCASE_INDEX))
             ff.write("{:05.2f},{:05.2f};{:3.1f},{:3.1f},{:3.1f}\n".format(particle.elements[0].pos.x,particle.elements[0].pos.y,particle.color[0],particle.color[1],particle.color[2]))
         ff.close()
 
@@ -649,6 +655,8 @@ class Painter(Widget):
                 candidate=Cross(pos.x,pos.y,color=color)
             elif particle_type==DISK_INDEX:
                 candidate=Disk(pos.x,pos.y,color=color)
+            elif particle_type==STAIRCASE_INDEX:
+                candidate=Staircase(pos.x,pos.y,color=color)
             else:
                 print("warning: ignoring line "+str(i)+" in file '"+file+"': unrecognized particle type: '"+entries[0]+"'",file=sys.stderr)
                 continue
@@ -702,5 +710,6 @@ class Painter(Widget):
 # global variables (used like precompiler variables)
 CROSS_INDEX=1
 DISK_INDEX=2
+STAIRCASE_INDEX=2
 
 
diff --git a/src/polyomino.py b/src/polyomino.py
index 126a3d2..e8fdf27 100644
--- a/src/polyomino.py
+++ b/src/polyomino.py
@@ -123,3 +123,32 @@ class Cross(Polyomino):
 class Disk(Polyomino):
     def __init__(self,x,y,**kwargs):
         super(Disk,self).__init__(**kwargs,elements=[Element_circle(x,y,size=kwargs.get("size",1.0))])
+
+# 3-staircase
+class Staircase(Polyomino):
+    def __init__(self,x,y,**kwargs):
+        super(Staircase,self).__init__(**kwargs,elements=[\
+        Element_square(x,y+1,1,aspect=3),\
+        Element_square(x+1,y,1),\
+        Element_square(x+1,y+1,1),\
+        Element_square(x+2,y,1)\
+        ])
+
+    # redefine stroke to avoid lines between touching elements
+    def stroke(self,painter):
+        # convert to graphical coordinates
+        coordx=painter.pos_tocoord_x(self.elements[0].pos.x)
+        coordy=painter.pos_tocoord_y(self.elements[0].pos.y)
+
+        Color(1,1,1)
+        Line(points=(
+        *(coordx-0.5*painter.base_size,coordy-1.5*painter.base_size),
+        *(coordx+2.5*painter.base_size,coordy-1.5*painter.base_size),
+        *(coordx+2.5*painter.base_size,coordy-0.5*painter.base_size),
+        *(coordx+1.5*painter.base_size,coordy-0.5*painter.base_size),
+        *(coordx+1.5*painter.base_size,coordy+0.5*painter.base_size),
+        *(coordx+0.5*painter.base_size,coordy+0.5*painter.base_size),
+        *(coordx+0.5*painter.base_size,coordy+1.5*painter.base_size),
+        *(coordx-0.5*painter.base_size,coordy+1.5*painter.base_size),
+        *(coordx-0.5*painter.base_size,coordy-1.5*painter.base_size),
+        ))