- * ___ X-2 ___ X-1 ___ 0 ___ 1 ___ 2 ___ 3 ___ 4 __
- * Y-1 Y-1 0 0 0 0 0
- * / \ / \ / \ / \ / \ / \ / \
- * / \ / \ / \ / \ / \ / \ / \
- * X-3 ___ X-2 ___ X-1 ___ 0 ___ 1 ___ 2 ___ 3 ___ 4
- * Y-2 Y-2 Y-2 1 1 1 1 1
- * \ / \ / \ / \ / \ / \ / \ /
- * \ / \ / \ / \ / \ / \ / \ /
- * ___ X-3 ___ X-2 ___ X-1 ___ 0 ___ 1 ___ 2 ___ 3 __
- * Y-3 Y-3 Y-3 2 2 2 2
- *
- * . . . . . . . . . . . . . . .
- *
- * X-4 ___ X-3 ___ X-2 ___ X-1 ___ 0 ___ 1 ___ 2 ___ 3
- * 1 1 1 1 Y-2 Y-2 Y-2 Y-2
- * \ / \ / \ / \ / \ / \ / \ /
- * \ / \ / \ / \ / \ / \ / \ /
- * ___ X-4 ___ X-3 ___ X-2 ___ X-1 ___ 0 ___ 1 ___ 2 __
- * 0 0 0 0 Y-1 Y-1 Y-1
+ * :axis of symmetry
+ * | :
+ * | :
+ * ___ X-2 ___ X-1 ___| 0 ___ 1 ___ 2 ___ 3 ___ 4 __
+ * Y-1 Y-1 |0: 0 0 0 0
+ * / \ / \ / :\ / \ / \ / \ / \
+ * / \ / \ /| : \ / \ / \ / \ / \
+ * X-3 ___ X-2 ___ X-1|___ 0 ___ 1 ___ 2 ___ 3 ___ 4
+ * Y-2 Y-2 Y-2| : 1 1 1 1 1
+ * \ / \ / \| : / \ / \ / \ / \ /
+ * \ / \ / \ :/ \ / \ / \ / \ /
+ * ___ X-2 ___ X-1 ___| 0 ___ 1 ___ 2 ___ 3 __ 4 ___
+ * Y-3 Y-3 |2: 2 2 2 2
+ * / \ / \ / :\ / \ / \ / \ / \
+ * / \ / \ /| : \ / \ / \ / \ / \
+ * X-3 ___ X-2 ___ X-1|___ 0 ___ 1 ___ 2 ___ 3 ___ 4
+ * Y-4 Y-4 Y-4| : 3 3 3 3 3
+ * | :
+ * . . . . .| :. . . . . . . . . .
+ * | :
+ * ___ X-2 ___ X-1 ___| 0 ___ 1 ___ 2 ___ 3 ___ 4 ___
+ * 2 2 |Y-3 Y-3 Y-3 Y-3 Y-3
+ * / \ / \ / :\ / \ / \ / \ / \
+ * / \ / \ /| : \ / \ / \ / \ / \
+ * __ X-2 ___ X-1|___ 0 ___ 1 ___ 2 ___ 3 ___ 3 ___ 4
+ * 1 1 | : Y-2 Y-2 Y-2 Y-2 Y-2 Y-2
+ * / \ / \ / \| : / \ / \ / \ / \ /
+ * / \ / \ / \ :/ \ / \ / \ / \ /
+ * -3 ___ X-2 ___ X-1 ___| 0 ___ 1 ___ 2 ___ 3 ___ 4 ___
+ * 0 0 0 |Y-1 Y-1 Y-1 Y-1 Y-1
+ * | :
+ * | :
+ * |
+ * ^ join, where there is
+ * a discontinuity in numbering