Add ZIGZAG example from Högberg et.al.

# 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.

Block 0: R, bot, L

Block 1: r

Block 2: l