Add diamond example

diff --git a/examples/diamond.py b/examples/diamond.py
new file mode 100755 (executable)
index 0000000..148cdca
--- /dev/null
+++ b/examples/diamond.py
@@ -0,0 +1,9 @@
+#!/usr/bin/env python3
+
+from pypol import *
+
+x, y = symbols('x y')
+diam = Ge(y, x - 1) & Le(y, x + 1) & Ge(y, -x - 1) & Le(y, -x + 1)
+print('diamond:', diam)
+print('projected on x:', diam.drop_dims('y'))
+