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diff --git a/2020/sketch_2020_01_31a/sketch_2020_01_31a.pyde b/2020/sketch_2020_01_31a/sketch_2020_01_31a.pyde
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+"""
+Number of possible triangles: 516
+Cols: 43 Rows: 12
+"""
+
+add_library('pdf')
+from itertools import product, combinations
+
+SPACE, BORDER = 20, 20
+
+def setup():
+    """Prepare screen or SVG and geometry."""
+    global triangles, W, H
+    size(900, 280)  # used to debug on screen
+    # size(900, 280, PDF, "43x12.pdf") # export
+    strokeJoin(ROUND)
+    # Calculate all 3-point combinations on a 4x4 grid
+    grid_points = product((-1, 0, 1, 2), repeat=2)
+    point_triples = combinations(grid_points, 3)
+    # Identify triangles (discard colinear point triples with zero area)
+    triangles = []
+    for pt in point_triples:
+        area = (pt[1][0] * (pt[2][1] - pt[0][1]) +
+                pt[2][0] * (pt[0][1] - pt[1][1]) +
+                pt[0][0] * (pt[1][1] - pt[2][1]))
+        if area != 0:
+            triangles.append(pt)
+    println("Number of possible triangles: {}"
+            .format(len(triangles)))
+    # Calculate the display grid dimensions
+    W = (width - BORDER * 2) // SPACE
+    H = (height - BORDER * 2) // SPACE
+    println("Cols: {} Rows: {}"
+            .format(W, H))
+    global i
+    i = 0
+
+def draw():
+    """Draw geometry."""
+    global i
+    background(240)
+    for y in range(H):
+        for x in range(W):
+            if i < len(triangles):
+                pushMatrix()
+                translate(BORDER + SPACE / 2 + SPACE * x,
+                          BORDER + SPACE / 2 + SPACE * y)
+                fill(0)
+                draw_poly(scale_poly(triangles[i], SPACE * .33))
+                popMatrix()
+                i += 1
+    # exit()
+    noLoop()
+
+def keyPressed():
+    saveFrame("{}triangles.png".format(len(triangles)))
+            
+
+def draw_poly(p_list, closed=True):
+    """Draw a polygon from a list of points (vectors or tuples)."""
+    beginShape()
+    for p in p_list:
+        if len(p) == 2 or p[2] == 0:
+            vertex(p[0], p[1])
+        else:
+            vertex(*p)
+    if closed:
+        endShape(CLOSE)
+    else:
+        endShape()
+
+
+def lerp_poly(p0, p1, t):
+    """Create interpolated version of poly - using tuples for points """
+    return [tuple(lerp(c0, c1, t) for c0, c1 in zip(sp0, sp1))
+            for sp0, sp1 in zip(p0, p1)]
+
+
+def scale_poly(p_list, s):
+    """Return a scaled version of a list of points (as tuples)."""
+    return [(p[0] * s, p[1] * s) for p in p_list]