\(q\stackrel{c}{\longrightarrow} x_c\)
\(x_c\stackrel{a}{\longrightarrow} z_a\)
\(x_c\stackrel{b}{\longrightarrow} z_b\)
\(x_c\stackrel{c}{\longrightarrow} x_{cc}\)
\(x_{cc}\stackrel{a}{\longrightarrow} z_a\)
\(x_{cc}\stackrel{b}{\longrightarrow} z_b\)
\(z_a\stackrel{c}{\longrightarrow} z_c\)
\(z_a\stackrel{a}{\longrightarrow} z_a\)
\(z_a\stackrel{b}{\longrightarrow} z_b\)
\(z_b\stackrel{a}{\longrightarrow} z_a\)
\(z_b\stackrel{b}{\longrightarrow} z_b\)