Add ZIGZAG example from Högberg et.al.

examples/zigzag

+# An automaton that recognizes the tree series ZIGZAG, which is defined as
+# follows:
+#
+# The alphabet Σ = {a/0, s/2} and ZIGZAG maps trees over Σ to ℕ:
+#
+#  ZIGZAG(a)             = 1
+#  ZIGZAG(s(a, _))       = 2
+#  ZIGZAG(s(s(_, t), _)) = 2 + ZIGZAG(t)
+#
+# Source: [1, Example 17]
+#
+# FIXME: R should really be Z, but there is at the time of writing a parser bug
+# in Z^X. (See https://git8.cs.fau.de/software/copar/issues/4)
+
+Z × R^({a} + X×X)
+
+l:   (1, { inj0 a: 1, inj1 (R, bot): 1, inj1 (r, bot): 1 })
+r:   (0, { inj0 a: 1, inj1 (bot, L): 1, inj1 (bot, l): 1 })
+L:   (0, { inj0 a: 1, inj1 (R, bot): 1 })
+R:   (0, { inj0 a: 1, inj1 (bot, L): 1 })
+bot: (0, { inj0 a: 1, inj1 (bot, bot): 1 })
+
+
+# [1]: Högberg, Johanna, Andreas Maletti, and Jonathan May. “Bisimulation
+# Minimisation for Weighted Tree Automata.” In Developments in Language Theory,
+# Berlin, Heidelberg: Springer Berlin Heidelberg, 2007.
+# https://doi.org/10.1007/978-3-540-73208-2_23.

examples/zigzag.out

+Block 0: R, bot, L
+Block 1: r
+Block 2: l