diff --git a/2020/sketch_2020_08_13a/arcs.py b/2020/sketch_2020_08_13a/arcs.py
new file mode 100644
index 00000000..68ef4f26
--- /dev/null
+++ b/2020/sketch_2020_08_13a/arcs.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+
+ROTATION = {0: 0,
+            BOTTOM: 0,
+            DOWN: 0,
+            1: HALF_PI,
+            LEFT: HALF_PI,
+            2: PI,
+            TOP: PI,
+            UP: PI,
+            3: PI + HALF_PI,
+            RIGHT: PI + HALF_PI,
+            BOTTOM + RIGHT: 0,
+            DOWN + RIGHT: 0,
+            DOWN + LEFT: HALF_PI,
+            BOTTOM + LEFT: HALF_PI,
+            TOP + LEFT: PI,
+            UP + LEFT: PI,
+            TOP + RIGHT: PI + HALF_PI,
+            UP + RIGHT: PI + HALF_PI,
+            }
+
+def quarter_circle(x, y, radius, quadrant):
+    circle_arc(x, y, radius, ROTATION[quadrant], HALF_PI)
+
+def half_circle(x, y, radius, quadrant):
+    circle_arc(x, y, radius, ROTATION[quadrant], PI)
+
+def circle_arc(x, y, radius, start_ang, sweep_ang):
+    arc(x, y, radius * 2, radius * 2, start_ang, start_ang + sweep_ang)
+
+def poly_arc(x, y, radius, start_ang, sweep_ang, num_points=2):
+    angle = sweep_ang / int(num_points)
+    a = start_ang
+    with beginShape():
+        while a <= start_ang + sweep_ang:
+            sx = x + cos(a) * radius
+            sy = y + sin(a) * radius
+            vertex(sx, sy)
+            a += angle
+
+def arc_poly(x, y, d, _, start_ang, end_ang, num_points=5):
+    sweep_ang = end_ang - start_ang
+    angle = sweep_ang / int(num_points)
+    a = start_ang
+    with beginShape():
+        while a <= end_ang:
+            sx = x + cos(a) * d / 2
+            sy = y + sin(a) * d / 2
+            vertex(sx, sy)
+            a += angle
+
+def bar(x1, y1, x2, y2, thickness=None, shorter=0, ends=(1, 1)):
+    """
+    O código para fazer as barras, dois pares (x, y),
+    um parâmetro de encurtamento: shorter
+    """
+    L = dist(x1, y1, x2, y2)
+    if not thickness:
+        thickness = 10
+    with pushMatrix():
+        translate(x1, y1)
+        angle = atan2(x1 - x2, y2 - y1)
+        rotate(angle)
+        offset = shorter / 2
+        line(thickness / 2, offset, thickness / 2, L - offset)
+        line(-thickness / 2, offset, -thickness / 2, L - offset)
+        if ends[0]:
+            half_circle(0, offset, thickness / 2, UP)
+        if ends[1]:
+            half_circle(0, L - offset, thickness / 2, DOWN)
+
+def var_bar(p1x, p1y, p2x, p2y, r1, r2=None):
+    if r2 is None:
+        r2 = r1
+    d = dist(p1x, p1y, p2x, p2y)
+    if d > 0:
+        with pushMatrix():
+            translate(p1x, p1y)
+            angle = atan2(p1x - p2x, p2y - p1y)
+            rotate(angle + HALF_PI)
+            ri = r1 - r2
+            beta = asin(ri / d) + HALF_PI
+            x1 = cos(beta) * r1
+            y1 = sin(beta) * r1
+            x2 = cos(beta) * r2
+            y2 = sin(beta) * r2
+            with pushStyle():
+                noStroke()
+                beginShape()
+                vertex(-x1, -y1)
+                vertex(d - x2, -y2)
+                vertex(d, 0)
+                vertex(d - x2, +y2)
+                vertex(-x1, +y1)
+                vertex(0, 0)
+                endShape(CLOSE)
+            line(-x1, -y1, d - x2, -y2)
+            line(-x1, +y1, d - x2, +y2)
+            arc(0, 0, r1 * 2, r1 * 2,
+                -beta - PI, beta - PI)
+            arc(d, 0, r2 * 2, r2 * 2,
+                beta - PI, PI - beta)
+    else:
+        ellipse(p1x, p1y, r1 * 2, r1 * 2)
+        ellipse(p2y, p2x, r2 * 2, r2 * 2)
diff --git a/2020/sketch_2020_08_13a/graph.py b/2020/sketch_2020_08_13a/graph.py
new file mode 100644
index 00000000..412493fa
--- /dev/null
+++ b/2020/sketch_2020_08_13a/graph.py
@@ -0,0 +1,302 @@
+#*- coding: utf-8 -*-
+
+"""
+A simple Python graph class, demonstrating the essential facts and functionalities of graphs
+based on https://www.python-course.eu/graphs_python.php and https://www.python.org/doc/essays/graphs/
+"""
+
+from random import choice
+
+class Graph(object):
+
+    def __init__(self, graph_dict=None):
+        """
+        Initialize a graph object with dictionary provided,
+        if none provided, create an empty one.
+        """
+        if graph_dict is None:
+            graph_dict = {}
+        self.__graph_dict = graph_dict
+
+    def __len__(self):
+        return len(self.__graph_dict)
+    
+    def vertices(self):
+        """Return the vertices of graph."""
+        return list(self.__graph_dict.keys())
+
+    def edges(self):
+        """Return the edges of graph """
+        return self.__generate_edges()
+
+    def add_vertex(self, vertex):
+        """
+        If the vertex "vertex" is not in self.__graph_dict,
+        add key "vertex" with an empty list as a value,
+        otherwise, do nothing.
+        """
+        if vertex not in self.__graph_dict:
+            self.__graph_dict[vertex] = []
+
+    def add_edge(self, edge):
+        """
+        Assuming that edge is of type set, tuple or list;
+        add edge between vertices. Can add multiple edges!
+        """
+        edge = set(edge)
+        vertex1 = edge.pop()
+        if edge:
+            # not a loop
+            vertex2 = edge.pop()
+            if vertex1 in self.__graph_dict:
+                self.__graph_dict[vertex1].append(vertex2)
+            else:
+                self.__graph_dict[vertex1] = [vertex2]
+            if vertex2 in self.__graph_dict:
+                self.__graph_dict[vertex2].append(vertex1)
+            else:
+                self.__graph_dict[vertex2] = [vertex1]
+        else:
+            # a loop
+            if vertex1 in self.__graph_dict:
+                self.__graph_dict[vertex1].append(vertex1)
+            else:
+                self.__graph_dict[vertex1] = [vertex1]        
+
+    def remove_vertex(self, vert):
+        del self.__graph_dict[vert]
+        for k in self.__graph_dict.keys():
+            if vert in self.__graph_dict[k]:
+                self.__graph_dict[k].remove(vert)
+      
+    def remove_edge(self, edge):
+        edge = set(edge)
+        vertex1 = edge.pop()
+        if edge:
+            vertex2 = edge.pop()
+            self.__graph_dict[vertex1].remove(vertex2)
+            self.__graph_dict[vertex2].remove(vertex1)
+        else:
+            self.__graph_dict[vertex1].remove(vertex1)
+
+    def __generate_edges(self):
+        """
+        Generate the edges, represented as sets with one
+        (a loop back to the vertex) or two vertices.
+        """
+        edges = []
+        for vertex in self.__graph_dict:
+            for neighbour in self.__graph_dict[vertex]:
+                if {neighbour, vertex} not in edges:
+                    edges.append({vertex, neighbour})
+        return edges
+
+    def __str__(self):
+        res = "vertices: "
+        for k in self.__graph_dict:
+            res += str(k) + " "
+        res += "\nedges: "
+        for edge in self.__generate_edges():
+            res += str(edge) + " "
+        return res
+
+    def find_isolated_vertices(self):
+        """
+        Return a list of isolated vertices.
+        """
+        graph = self.__graph_dict
+        isolated = []
+        for vertex in graph:
+            print(isolated, vertex)
+            if not graph[vertex]:
+                isolated += [vertex]
+        return isolated
+
+    def find_path(self, start_vertex, end_vertex, path=[]):
+        """
+        Find a path from start_vertex to end_vertex in graph.
+        """
+        graph = self.__graph_dict
+        path = path + [start_vertex]
+        if start_vertex == end_vertex:
+            return path
+        if start_vertex not in graph:
+            return None
+        for vertex in graph[start_vertex]:
+            if vertex not in path:
+                extended_path = self.find_path(vertex,
+                                               end_vertex,
+                                               path)
+                if extended_path:
+                    return extended_path
+        return None
+
+    def find_all_paths(self, start_vertex, end_vertex, path=[]):
+        """
+        Find all paths from start_vertex to end_vertex.
+        """
+        graph = self.__graph_dict
+        path = path + [start_vertex]
+        if start_vertex == end_vertex:
+            return [path]
+        if start_vertex not in graph:
+            return []
+        paths = []
+        for vertex in graph[start_vertex]:
+            if vertex not in path:
+                extended_paths = self.find_all_paths(vertex,
+                                                     end_vertex,
+                                                     path)
+                for p in extended_paths:
+                    paths.append(p)
+        return paths
+
+    def is_connected(self,
+                     vertices_encountered=None,
+                     start_vertex=None):
+        """Find if the graph is connected."""
+        if vertices_encountered is None:
+            vertices_encountered = set()
+        gdict = self.__graph_dict
+        vertices = list(gdict.keys())  # "list" necessary in Python 3
+        if not start_vertex:
+            # chosse a vertex from graph as a starting point
+            start_vertex = vertices[0]
+        vertices_encountered.add(start_vertex)
+        if len(vertices_encountered) != len(vertices):
+            for vertex in gdict[start_vertex]:
+                if vertex not in vertices_encountered:
+                    if self.is_connected(vertices_encountered, vertex):
+                        return True
+        else:
+            return True
+        return False
+
+    def vertex_degree(self, vertex):
+        """
+        Return the number of edges connecting to a vertex (the number of adjacent vertices).
+        Loops are counted double, i.e. every occurence of vertex in the list of adjacent vertices.
+        """
+        adj_vertices = self.__graph_dict[vertex]
+        degree = len(adj_vertices) + adj_vertices.count(vertex)
+        return degree
+
+    def degree_sequence(self):
+        """Calculates the degree sequence."""
+        seq = []
+        for vertex in self.__graph_dict:
+            seq.append(self.vertex_degree(vertex))
+        seq.sort(reverse=True)
+        return tuple(seq)
+
+    @staticmethod
+    def is_degree_sequence(sequence):
+        """
+        Return True, if the sequence is a degree sequence (non-increasing),
+        otherwise return False.
+        """
+        return all(x >= y for x, y in zip(sequence, sequence[1:]))
+
+    def delta(self):
+        """Find minimum degree of vertices."""
+        min = 100000000
+        for vertex in self.__graph_dict:
+            vertex_degree = self.vertex_degree(vertex)
+            if vertex_degree < min:
+                min = vertex_degree
+        return min
+
+    def Delta(self):
+        """Finde maximum degree of vertices."""
+        max = 0
+        for vertex in self.__graph_dict:
+            vertex_degree = self.vertex_degree(vertex)
+            if vertex_degree > max:
+                max = vertex_degree
+        return max
+
+    def density(self):
+        """Calculate the graph density."""
+        g = self.__graph_dict
+        V = len(g.keys())
+        E = len(self.edges())
+        return 2.0 * E / (V * (V - 1))
+
+    def diameter(self):
+        """Calculates the graph diameter."""
+
+        v = self.vertices()
+        pairs = [
+            (v[i],
+             v[j]) for i in range(
+                len(v)) for j in range(
+                i + 1,
+                len(v) - 1)]
+        smallest_paths = []
+        for (s, e) in pairs:
+            paths = self.find_all_paths(s, e)
+            smallest = sorted(paths, key=len)[0]
+            smallest_paths.append(smallest)
+
+        smallest_paths.sort(key=len)
+
+        # longest path is at the end of list,
+        # i.e. diameter corresponds to the length of this path
+        diameter = len(smallest_paths[-1]) - 1
+        return diameter
+
+    @staticmethod
+    def erdoes_gallai(dsequence):
+        """
+        Check if Erdoes-Gallai inequality condition is fullfilled.
+        """
+        if sum(dsequence) % 2:
+            # sum of sequence is odd
+            return False
+        if Graph.is_degree_sequence(dsequence):
+            for k in range(1, len(dsequence) + 1):
+                left = sum(dsequence[:k])
+                right = k * (k - 1) + sum([min(x, k) for x in dsequence[k:]])
+                if left > right:
+                    return False
+        else:
+            # sequence is increasing
+            return False
+        return True
+
+
+    # Code by Eryk Kopczyński
+    def find_shortest_path(self, start, end):
+        from collections import deque
+        graph = self.__graph_dict
+        dist = {start: [start]}
+        q = deque((start,))
+        while len(q):
+            at = q.popleft()
+            for next in graph[at]:
+                if next not in dist:
+                    #dist[next] = [dist[at], next] 
+                    dist[next] = dist[at]+[next]   # less efficient but nicer output
+                    q.append(next)
+        return dist.get(end)
+    
+    
+    def get_random_vertex(self):
+        return choice(self.vertices())
+    
+    @staticmethod            
+    def random_graph(names, connect_rate=.9, allow_loops=True, connected=False):
+        vertices = set(names)
+        while True:
+            graph = Graph()
+            for v in vertices:
+                graph.add_vertex(v)
+                if random(1) < connect_rate:
+                    if allow_loops:
+                        names = list(vertices)
+                    else:
+                        names = list(vertices - set((v,)))
+                    graph.add_edge({v, choice(names)})    
+            if not connected or graph.is_connected():
+                break                    
+        return graph
diff --git a/2020/sketch_2020_08_13a/grid.py b/2020/sketch_2020_08_13a/grid.py
new file mode 100644
index 00000000..e08d33aa
--- /dev/null
+++ b/2020/sketch_2020_08_13a/grid.py
@@ -0,0 +1,77 @@
+#*- coding: utf-8 -*-
+
+from __future__ import division, print_function
+from random import sample, choice
+
+
+def setup_grid(graph, width, height, margin=None):
+    global w, h
+    margin = margin or width / 40
+    cols, rows = dim_grid(len(graph))
+    w, h = (width - margin * 2) / cols, (height - margin * 2) / rows
+    points = []
+    for i in range(cols * rows):
+        c = i % cols
+        r = i // rows
+        x = margin + w * 0.5 + c * w - 14 * (r % 2) + 7
+        y = margin + h * 0.5 + r * h - 14 * (c % 2) + 7
+        z = 0
+        points.append([x, y, z])
+    points = sorted(
+        points, key=lambda p: dist(p[0], p[1], width / 2, height / 2))
+    v_list = reversed(sorted(graph.vertices(), key=graph.vertex_degree))
+    # v_list = sorted(graph.vertices(), key=graph.vertex_degree)
+    grid = {v: p for v, p in zip(v_list, points)}
+    for k in grid.keys():
+        grid[k][2] = (w / 10) * graph.vertex_degree(k)
+    return grid
+
+def dim_grid(n):
+    a = int(sqrt(n))
+    b = n // a
+    if a * b < n:
+        b += 1
+    print(u'{}: {} × {} ({})'.format(n, a, b, a * b))
+    return a, b
+
+def edge_distances(graph, grid):
+    total = 0
+    for edge in graph.edges():
+        if len(edge) == 2:
+            a, b = edge
+            d = PVector.dist(PVector(*grid[a]),
+                             PVector(*grid[b]))
+            total += d
+    return total
+
+def grid_swap(graph, grid, display_text, num=2):
+    fail = 0
+    n = m = edge_distances(graph, grid)
+    while m <= n and fail < len(graph) ** 2:
+        new_grid = dict(grid)
+        if num == 2:
+            a, b = sample(graph.vertices(), 2)
+            new_grid[a], new_grid[b] = new_grid[b], new_grid[a]
+        else:
+            ks = sample(graph.vertices(), num)
+            vs = [grid[k] for k in sample(ks, num)]
+            for k, v in zip(ks, vs):
+                new_grid[k] = v
+        n = edge_distances(graph, new_grid)
+        if m > n:
+            t = "{:.2%} at: {} tries of {}v shuffle/swap" \
+                .format((n - m) / m, fail + 1, num)
+            display_text.append(t)
+            print("\n" + t, end="")
+            for k in new_grid.keys():
+                new_grid[k][2] = (w / 10) * graph.vertex_degree(k)
+            return new_grid
+        else:
+            fail += 1
+    print(".", end='')
+    return grid
+
+def v_dist(a, b):
+    xa, ya, _ = a
+    xb, yb, _ = b
+    return dist(xa, ya, xb, yb)
diff --git a/2020/sketch_2020_08_13a/sketch_2020_08_13a.pyde b/2020/sketch_2020_08_13a/sketch_2020_08_13a.pyde
new file mode 100644
index 00000000..d06616be
--- /dev/null
+++ b/2020/sketch_2020_08_13a/sketch_2020_08_13a.pyde
@@ -0,0 +1,164 @@
+from __future__ import print_function, division
+from random import choice
+from graph import Graph
+from grid import *  # setup_grid, grid_swap, edge_distances
+from arcs import var_bar
+
+thread_count = 0
+gx, gy = 0, 100
+viz_stat = False
+
+def setup():
+    size(400, 400)
+    colorMode(HSB)
+    textAlign(CENTER, CENTER)
+    f = createFont("Source Code Pro Bold", 12)
+    textFont(f)
+    setup_graph()
+
+def setup_graph():
+    # create a random graph and a dict of grid postions for its vertices
+    global graph, grid, m, d, display_text
+    graph = Graph.random_graph(range(49), allow_loops=False, connected=True)
+    grid = setup_grid(graph, width=width, height=width, margin=10)
+    # display setup
+    display_text = [""]
+    m = edge_distances(graph, grid)  # "metric", sum of edge distances
+    d = createGraphics(width, 100)  # canvas for data display
+    d.beginDraw()
+    d.background(150)
+    d.endDraw()
+    print(graph)
+    # setup walker
+    global sel_v, path_walker, t_walker
+    sel_v = graph.get_random_vertex()
+    path_walker = []
+    t_walker = 0
+
+def draw():
+    background(200)
+    noFill()
+    for e in graph.edges():
+        va = e.pop()
+        xa, ya, za = grid[va]
+        if len(e) == 1:
+            vb = e.pop()
+            xb, yb, zb = grid[vb]
+            noStroke()
+            fill(((za + zb) / 2) * 12, 255, 255, 128)
+            var_bar(xa, ya, xb, yb, za, zb)
+
+    for v in grid.keys():
+        x, y, z = grid[v]
+        fill(64)        
+        circle(x, y, 10)
+        if keyPressed:
+            fill(0)
+            text("{}".format(v).upper(), x - 15, y - 5)    
+
+    walker()
+    this.surface.setResizable(False)
+    if viz_stat:
+        image(d, 0, height - 100)
+        fill(0)
+        textAlign(LEFT)
+        text(format(gy / 100, ".2%"), width - 100, height - 80)
+        text(format(m, ".0f"), width - 100, height - 60)
+        fill(255)
+        text('\n'.join(display_text[-2:]), 20, height - 40)
+    
+def display():
+    d.beginDraw()
+    d.stroke(0)
+    d.strokeWeight(1)
+    d.line(gx, 100, gx, 100 - gy)
+    d.noStroke()
+    d.endDraw()
+
+def walker():
+    global t_walker, path_walker, sel_v
+    if path_walker and t_walker < 1:
+        path_vectors = [PVector(*grid[pv]) for pv in path_walker]
+        p = lerpVectors(t_walker, path_vectors)
+        noFill()
+        stroke(255)
+        circle(p.x, p.y, p.z)
+        t_walker += .03 / len(path_walker)
+    else:
+        path_walker = []
+        noStroke()
+        fill(255)
+        x, y, z = grid[sel_v]
+        circle(x, y, 10)
+
+def lerpVectors(amt, vecs):
+    """ from Jeremy Douglass """
+    amt = constrain(amt, 0, 1)  # let's play safe
+    if len(vecs) == 1:
+        return vecs[0]
+    cunit = 1.0 / (len(vecs) - 1)
+    return PVector.lerp(vecs[floor(amt / cunit)],
+                        vecs[ceil(amt / cunit)],
+                        amt % cunit / cunit)
+
+def keyTyped():
+    global gx, gy, viz_stat
+    if key == 'r':
+        setup_graph()
+        background(200)
+        gx, gy = 0, 100
+    elif key == 'v':
+        viz_stat = not viz_stat
+        this.surface.setResizable(True)
+        if viz_stat:
+            this.surface.setSize(400, 500)    
+        else:
+            this.surface.setSize(400, 400)                
+
+    else:
+        thread("swapping")
+
+def swapping():
+    global grid, thread_count, gx, gy, m, t
+    if str(key) not in 'sc23456789':
+        return
+    thread_count += 1
+    this_thread, this_key = thread_count, str(key)
+    m = edge_distances(graph, grid)
+    t = "Starting thread:{} key:{}".format(this_thread, key)
+    display_text.append(t)
+    print("\n" + t, end="")
+    len_graph = len(graph)
+    for _ in range(len_graph):
+        if this_key == 's':
+            grid = grid_swap(graph, grid, display_text, num=len_graph)
+        if this_key in '234556789':
+            grid = grid_swap(graph, grid, display_text, num=int(this_key))
+        n = edge_distances(graph, grid)
+        gx += 1
+        if n < m:
+            gy -= gy * (m - n) / m
+            m = n
+        display()
+        if key == 'k':
+            break
+    t = "Ending thread: {}".format(this_thread)
+    display_text.append(t)
+    print("\n" + t, end="")
+
+
+def mousePressed():
+    global path_walker, t_walker, sel_v
+    for v in graph.vertices():
+        x, y, _ = grid[v]
+        if v != sel_v and dist(x, y, mouseX, mouseY) < 10:
+            path = graph.find_shortest_path(sel_v, v)
+            if path:
+                path_walker = path
+                t_walker = 0
+                sel_v = v
+                
+# TODO IDEAS: 
+# Show what "nearby" sample means
+# Find distance outliers and try to shuffle them closer
+# Run many times without visualisation on Python 3 to get some huge samples