gh-35331: Add monotile to polgyon examples

    
This adds an aperiodic monotile to the many examples in the
documentation of the `polygon2d` function.
https://arxiv.org/abs/2303.10798

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URL: #35331
Reported by: Moritz Firsching
Reviewer(s): Matthias Köppe

src/doc/en/reference/references/index.rst

@@ -5594,6 +5594,10 @@ REFERENCES:
              Journal of Cryptology. 12. 193-196. 1999.
              :doi:`10.1007/s001459900052`.
 
+.. [Smi2023] \D. Smith, J. S. Myers, C. S. Kaplan and C. Goodman-Strauss, 
+             *An aperiodic monotile*,
+             :arxiv:`2303.10798`
+
 .. [SP2010] Fernando Solano and Michal Pioro, *Lightpath Reconfiguration in WDM
             networks*, IEEE/OSA Journal of Optical Communication and Networking
             2(12):1010-1021, 2010. :doi:`10.1364/JOCN.2.001010`.

src/sage/plot/polygon.py

@@ -386,6 +386,21 @@ def polygon2d(points, **options):
         P = polygon2d(v, legend_label='some form')
         sphinx_plot(P)
 
+    An aperiodic monotile, [Smi2023]_::
+
+        sage: s = sqrt(3)
+        sage: polygon2d([[0, 0], [0, s], [1, s], [3/2, 3/2*s], [3, s], [3, 0], [4, 0],
+        ....:            [9/2, -1/2*s], [3, -s], [3/2, -1/2*s], [1, -s], [-1, -s],
+        ....:            [-3/2, -1/2*s]], axes=False)
+        Graphics object consisting of 1 graphics primitive
+
+    .. PLOT::
+
+        s = sqrt(3)
+        P = polygon2d([[0, 0], [0, s], [1, s], [3/2, 3/2*s], [3, s], [3, 0], [4, 0], [9/2, -1/2*s], [3, -s], \
+                       [3/2, -1/2*s], [1, -s], [-1, -s], [-3/2, -1/2*s]], axes=False)
+        sphinx_plot(P)
+
     A purple hexagon::
 
         sage: L = [[cos(pi*i/3),sin(pi*i/3)] for i in range(6)]