Support labeled edges

[fandreuz]

Labeled edges are ubiquitous in practical applications of bisimulation (concurrency theory [1], XML indexing [2])

[1]: Kanellakis, Paris C., and Scott A. Smolka. "CCS expressions, finite state processes, and three problems of equivalence." Information and computation 86.1 (1990): 43-68.
[2]: Yi, Ke, et al. "Incremental maintenance of XML structural indexes." Proceedings of the 2004 ACM SIGMOD international conference on Management of data. 2004.