diff --git a/cross.py b/cross.py
new file mode 100644
index 0000000..4e69c8d
--- /dev/null
+++ b/cross.py
@@ -0,0 +1,200 @@
+import math
+from kivy.graphics import Color,Line,Rectangle
+from kivy.uix.widget import Widget
+
+from point import Point
+
+class Cross():
+    # size of central square
+    size=50
+
+    def __init__(self,x,y,**kwargs):
+        self.pos=Point(x,y)
+        self.color=kwargs.get("color",(0,0,1))
+        self.selected=False
+
+    # set position
+    def setpos(self,x,y):
+        self.pos.x=x
+        self.pos.y=y
+
+    def draw(self):
+        # fill
+        #if not self.selected:
+        #    Color(*(self.color))
+        #else:
+        #    Color(1,0,0)
+        Color(*(self.color))
+        Rectangle(pos=(self.pos.x-self.size*1.5,self.pos.y-self.size*0.5),size=(3*self.size,self.size))
+        Rectangle(pos=(self.pos.x-self.size*0.5,self.pos.y-self.size*1.5),size=(self.size,3*self.size))
+
+        # stroke
+        Color(1,1,1)
+        Line(points=(
+        *(self.pos.x-self.size*0.5,self.pos.y-self.size*0.5),
+        *(self.pos.x-self.size*0.5,self.pos.y-self.size*1.5),
+        *(self.pos.x+self.size*0.5,self.pos.y-self.size*1.5),
+        *(self.pos.x+self.size*0.5,self.pos.y-self.size*0.5),
+        *(self.pos.x+self.size*1.5,self.pos.y-self.size*0.5),
+        *(self.pos.x+self.size*1.5,self.pos.y+self.size*0.5),
+        *(self.pos.x+self.size*0.5,self.pos.y+self.size*0.5),
+        *(self.pos.x+self.size*0.5,self.pos.y+self.size*1.5),
+        *(self.pos.x-self.size*0.5,self.pos.y+self.size*1.5),
+        *(self.pos.x-self.size*0.5,self.pos.y+self.size*0.5),
+        *(self.pos.x-self.size*1.5,self.pos.y+self.size*0.5),
+        *(self.pos.x-self.size*1.5,self.pos.y-self.size*0.5),
+        *(self.pos.x-self.size*0.5,self.pos.y-self.size*0.5),
+        ))
+
+    # check whether a cross at pos interacts with cross
+    def check_interaction(self,pos):
+        return ((pos-self.pos)/self.size).int()**2>=5
+
+    # find position along a line that comes in contact with the line going through pos in direction v
+    def move_on_line_to_stick(self,pos,v):
+        # relative to cross
+        return self.move_on_line_to_stick_relative((pos-self.pos)/self.size,v/self.size)*self.size+self.pos
+    def move_on_line_to_stick_relative(self,x,v):
+
+        # if x is in the right quadrant
+        if abs(x.y)<=x.x:
+            # find all stuck positions on lines
+            stuck=[]
+
+            # check intersections with vertical lines
+            if v.x!=0:
+                for i in range(1,4):
+                    # candidate
+                    y=Point(i,x.y+(i-x.x)*v.y/v.x)
+                    # check that it is in the right range
+                    if abs(y.y)<=4-i and abs(y.y)>=3-i:
+                        stuck.append(y)
+            # check intersections with horizontal lines
+            if v.y!=0:
+                for i in [-3,-2,-1,1,2,3]:
+                    # candidate
+                    y=Point(x.x+(i-x.y)*v.x/v.y,i)
+                    # check that it is in the right range
+                    if y.x<=4-abs(i) and y.x>=3-abs(i):
+                        stuck.append(y)
+
+            return x.closest(stuck)
+
+        # reflect other quadrants to the right one
+        # top quadrant
+        elif abs(x.x)<=x.y:
+            closest=self.move_on_line_to_stick_relative(Point(x.y,x.x),Point(v.y,v.x))
+            return Point(closest.y,closest.x)
+        # bottom quadrant
+        elif abs(x.x)<=-x.y:
+            closest=self.move_on_line_to_stick_relative(Point(-x.y,x.x),Point(-v.y,v.x))
+            return Point(closest.y,-closest.x)
+        # left quadrant
+        else:
+            closest=self.move_on_line_to_stick_relative(Point(-x.x,x.y),Point(-v.x,v.y))
+            return Point(-closest.x,closest.y)
+
+
+# L_infinity distance rescalled by 3 in the x direction
+def cross_distx(x,y):
+    return max(abs(x.x-y.x)/3,abs(x.y-y.y))
+# L_infinity distance rescalled by 3 in the y direction
+def cross_disty(x,y):
+    return max(abs(x.x-y.x),abs(x.y-y.y)/3)
+
+# polar description of touching cross
+def cross_polar(t):
+    # by symmetry, put angle in interval (-pi/4,pi/4), and take absolute value
+    tt=abs((t+math.pi/4)%(math.pi/2)-math.pi/4)
+    if tt<math.atan(1/3):
+        return 3/math.cos(tt)
+    elif tt<math.atan(1/2):
+        return 1/math.sin(tt)
+    else:
+        return 2/math.cos(tt)
+
+
+
+# cross painter
+class Cross_painter(Widget):
+
+    def __init__(self,**kwargs):
+
+        # list of crosses
+        self.crosses=[]
+
+        # selected cross
+        self.selected=None
+
+        # init Widget
+        super(Cross_painter,self).__init__(**kwargs)
+
+
+    # draw all crosses
+    def draw(self):
+        with self.canvas:
+            for cross in self.crosses:
+                cross.draw()
+
+
+    # respond to mouse down
+    def on_touch_down(self,touch):
+        # create new cross
+        if touch.button=="right":
+            if self.check_add(Point(touch.x,touch.y)):
+                new=Cross(touch.x,touch.y)
+                with self.canvas:
+                    new.draw()
+                # add to list
+                self.crosses.append(new)
+
+        # select cross
+        if touch.button=="left":
+            # unselect
+            if self.selected!=None:
+                self.selected.selected=False
+
+            # find cross under touch
+            self.selected=self.find_cross(Point(touch.x,touch.y))
+            # select
+            if self.selected!=None:
+                self.selected.selected=True
+
+
+    # respond to drag
+    def on_touch_move(self,touch):
+        # only move on left click
+        if touch.button=="left" and self.selected!=None:
+            self.selected.pos=self.check_move(Point(touch.x,touch.y),self.selected)
+            # redraw
+            self.canvas.clear()
+            self.draw()
+
+
+    # find the cross at position pos
+    def find_cross(self,pos):
+        for cross in self.crosses:
+            if cross_distx(pos,cross.pos)<=cross.size/2 or cross_disty(pos,cross.pos)<=cross.size/2:
+                return cross
+        # none found
+        return None
+
+    # check that a cross can move to new position
+    def check_move(self,newpos,cross):
+        for other in self.crosses:
+            # do not compare a cross to itself
+            if other!=cross:
+                # move would make cross overlap with other
+                if other.check_interaction(newpos)==False:
+                    # stick to the cross
+                    return other.move_on_line_to_stick(cross.pos,newpos-cross.pos)
+        return newpos
+
+    # check that a cross can be added at position
+    def check_add(self,pos):
+        for cross in self.crosses:
+            if cross.check_interaction(pos)==False:
+                return False
+        return True
+
+
diff --git a/jam.kv b/jam.kv
new file mode 100644
index 0000000..2e0feba
--- /dev/null
+++ b/jam.kv
@@ -0,0 +1,7 @@
+#: kivy 2.0.0
+
+#<jam>:
+#  canvas:
+#    Rectangle:
+#      pos: 0,0
+#      size: self.width,self.height
diff --git a/main.py b/main.py
index d34b69f..f22cccb 100644
--- a/main.py
+++ b/main.py
@@ -1,9 +1,9 @@
-import math
 from kivy.app import App
 from kivy.uix.widget import Widget
-from kivy.graphics import Color,Line,Rectangle
 from kivy.config import Config
 
+from cross import Cross,Cross_painter
+
 # App class
 class Jam_app(App):
     # name of .kv file for main interface
@@ -15,245 +15,6 @@ class Jam_app(App):
         parent.add_widget(self.cross_painter)
         return parent
 
-# cross painter
-class Cross_painter(Widget):
-
-    def __init__(self,**kwargs):
-
-        # list of crosses
-        self.crosses=[]
-
-        # selected cross
-        self.selected=None
-
-        # init Widget
-        super(Cross_painter,self).__init__(**kwargs)
-
-
-    # draw all crosses
-    def draw(self):
-        with self.canvas:
-            for cross in self.crosses:
-                cross.draw()
-
-
-    # respond to mouse down
-    def on_touch_down(self,touch):
-        # create new cross
-        if touch.button=="right":
-            if self.check_add(Point(touch.x,touch.y)):
-                new=Cross(touch.x,touch.y)
-                with self.canvas:
-                    new.draw()
-                # add to list
-                self.crosses.append(new)
-
-        # select cross
-        if touch.button=="left":
-            # unselect
-            if self.selected!=None:
-                self.selected.selected=False
-
-            # find cross under touch
-            self.selected=self.find_cross(Point(touch.x,touch.y))
-            # select
-            if self.selected!=None:
-                self.selected.selected=True
-
-
-    # respond to drag
-    def on_touch_move(self,touch):
-        # only move on left click
-        if touch.button=="left" and self.selected!=None:
-            self.selected.pos=self.check_move(Point(touch.x,touch.y),self.selected)
-            # redraw
-            self.canvas.clear()
-            self.draw()
-
-
-    # find the cross at position pos
-    def find_cross(self,pos):
-        for cross in self.crosses:
-            if cross_distx(pos,cross.pos)<=cross.size/2 or cross_disty(pos,cross.pos)<=cross.size/2:
-                return cross
-        # none found
-        return None
-
-    # check that a cross can move to new position
-    def check_move(self,newpos,cross):
-        for other in self.crosses:
-            # do not compare a cross to itself
-            if other!=cross:
-                if other.check_interaction(newpos)==False:
-                    # stick to the cross
-                    return other.move_on_line_to_stick(cross.pos,newpos-cross.pos)
-        return newpos
-
-    # check that a cross can be added at position
-    def check_add(self,pos):
-        for cross in self.crosses:
-            if cross.check_interaction(pos)==False:
-                return False
-        return True
-
-# cross
-class Cross():
-    # size of central square
-    size=50
-
-    def __init__(self,x,y,**kwargs):
-        self.pos=Point(x,y)
-        self.color=kwargs.get("color",(0,0,1))
-        self.selected=False
-
-    # set position
-    def setpos(self,x,y):
-        self.pos.x=x
-        self.pos.y=y
-
-    def draw(self):
-        # fill
-        #if not self.selected:
-        #    Color(*(self.color))
-        #else:
-        #    Color(1,0,0)
-        Color(*(self.color))
-        Rectangle(pos=(self.pos.x-self.size*1.5,self.pos.y-self.size*0.5),size=(3*self.size,self.size))
-        Rectangle(pos=(self.pos.x-self.size*0.5,self.pos.y-self.size*1.5),size=(self.size,3*self.size))
-
-        # stroke
-        Color(1,1,1)
-        Line(points=(
-        *(self.pos.x-self.size*0.5,self.pos.y-self.size*0.5),
-        *(self.pos.x-self.size*0.5,self.pos.y-self.size*1.5),
-        *(self.pos.x+self.size*0.5,self.pos.y-self.size*1.5),
-        *(self.pos.x+self.size*0.5,self.pos.y-self.size*0.5),
-        *(self.pos.x+self.size*1.5,self.pos.y-self.size*0.5),
-        *(self.pos.x+self.size*1.5,self.pos.y+self.size*0.5),
-        *(self.pos.x+self.size*0.5,self.pos.y+self.size*0.5),
-        *(self.pos.x+self.size*0.5,self.pos.y+self.size*1.5),
-        *(self.pos.x-self.size*0.5,self.pos.y+self.size*1.5),
-        *(self.pos.x-self.size*0.5,self.pos.y+self.size*0.5),
-        *(self.pos.x-self.size*1.5,self.pos.y+self.size*0.5),
-        *(self.pos.x-self.size*1.5,self.pos.y-self.size*0.5),
-        *(self.pos.x-self.size*0.5,self.pos.y-self.size*0.5),
-        ))
-
-    # check whether a cross at pos interacts with cross
-    def check_interaction(self,pos):
-        return ((pos-self.pos)/self.size).int()**2>=5
-
-    # find position along a line that comes in contact with the line going through pos in direction v
-    def move_on_line_to_stick(self,pos,v):
-        # relative to cross
-        return self.move_on_line_to_stick_relative((pos-self.pos)/self.size,v/self.size)*self.size+self.pos
-    def move_on_line_to_stick_relative(self,x,v):
-
-        # if x is in the right quadrant
-        if abs(x.y)<=x.x:
-            # find all stuck positions on lines
-            stuck=[]
-
-            # check intersections with vertical lines
-            if v.x!=0:
-                for i in range(1,4):
-                    # candidate
-                    y=Point(i,x.y+(i-x.x)*v.y/v.x)
-                    # check that it is in the right range
-                    if abs(y.y)<=4-i and abs(y.y)>=3-i:
-                        stuck.append(y)
-            # check intersections with horizontal lines
-            if v.y!=0:
-                for i in [-3,-2,-1,1,2,3]:
-                    # candidate
-                    y=Point(x.x+(i-x.y)*v.x/v.y,i)
-                    # check that it is in the right range
-                    if y.x<=4-abs(i) and y.x>=3-abs(i):
-                        stuck.append(y)
-
-            return x.closest(stuck)
-
-        # reflect other quadrants to the right one
-        # top quadrant
-        elif abs(x.x)<=x.y:
-            closest=self.move_on_line_to_stick_relative(Point(x.y,x.x),Point(v.y,v.x))
-            return Point(closest.y,closest.x)
-        # bottom quadrant
-        elif abs(x.x)<=-x.y:
-            closest=self.move_on_line_to_stick_relative(Point(-x.y,x.x),Point(-v.y,v.x))
-            return Point(closest.y,-closest.x)
-        # left quadrant
-        else:
-            closest=self.move_on_line_to_stick_relative(Point(-x.x,x.y),Point(-v.x,v.y))
-            return Point(-closest.x,closest.y)
-
-
-class Point:
-    def __init__(self,x,y):
-        self.x=x
-        self.y=y
-
-    def __add__(self,point):
-        return Point(self.x+point.x,self.y+point.y)
-
-    def __sub__(self,point):
-        return Point(self.x-point.x,self.y-point.y)
-
-    def __neg__(self):
-        return Point(-self.x,-self.y)
-
-    def __mul__(self,a):
-        return Point(a*self.x,a*self.y)
-
-    def __truediv__(self,a):
-        return Point(self.x/a,self.y/a)
-
-    def __pow__(self,a):
-        if a==2:
-            return self.dot(self)
-
-    # dot product
-    def dot(self,x):
-        return self.x*x.x+self.y*x.y
-
-    # integer part
-    def int(self):
-        return Point(int(self.x),int(self.y))
-
-    # find the closest among a list of points
-    def closest(self,points):
-        dist=math.inf
-        closest=None
-        for point in points:
-            if (self-point)**2<dist:
-                closest=point
-                dist=(self-point)**2
-        return closest
-
-# L_infinity distance rescalled by 3 in the x direction
-def cross_distx(x,y):
-    return max(abs(x.x-y.x)/3,abs(x.y-y.y))
-# L_infinity distance rescalled by 3 in the y direction
-def cross_disty(x,y):
-    return max(abs(x.x-y.x),abs(x.y-y.y)/3)
-
-# polar description of touching cross
-def cross_polar(t):
-    # by symmetry, put angle in interval (-pi/4,pi/4), and take absolute value
-    tt=abs((t+math.pi/4)%(math.pi/2)-math.pi/4)
-    if tt<math.atan(1/3):
-        return 3/math.cos(tt)
-    elif tt<math.atan(1/2):
-        return 1/math.sin(tt)
-    else:
-        return 2/math.cos(tt)
-
-
-# sign function
-def sgn(x):
-    if x>=0:
-        return 1
-    return -1
 
 
 # disable red circles on right click
diff --git a/point.py b/point.py
new file mode 100644
index 0000000..60ef0f3
--- /dev/null
+++ b/point.py
@@ -0,0 +1,45 @@
+import math
+
+# point in two dimensions
+class Point:
+    def __init__(self,x,y):
+        self.x=x
+        self.y=y
+
+    def __add__(self,point):
+        return Point(self.x+point.x,self.y+point.y)
+
+    def __sub__(self,point):
+        return Point(self.x-point.x,self.y-point.y)
+
+    def __neg__(self):
+        return Point(-self.x,-self.y)
+
+    def __mul__(self,a):
+        return Point(a*self.x,a*self.y)
+
+    def __truediv__(self,a):
+        return Point(self.x/a,self.y/a)
+
+    def __pow__(self,a):
+        if a==2:
+            return self.dot(self)
+
+    # dot product
+    def dot(self,x):
+        return self.x*x.x+self.y*x.y
+
+    # integer part
+    def int(self):
+        return Point(int(self.x),int(self.y))
+
+    # find the closest among a list of points
+    def closest(self,points):
+        dist=math.inf
+        closest=None
+        for point in points:
+            if (self-point)**2<dist:
+                closest=point
+                dist=(self-point)**2
+        return closest
+
diff --git a/tools.py b/tools.py
new file mode 100644
index 0000000..9882582
--- /dev/null
+++ b/tools.py
@@ -0,0 +1,6 @@
+
+# sign function
+def sgn(x):
+    if x>=0:
+        return 1
+    return -1