Causality podcast: http://thinkdistributed.io/blog/2013/08/28/causality.html
Lamport paper: http://cnlab.kaist.ac.kr/~ikjun/data/Course_work/CS642-Distributed_Systems/papers/lamport1978.pdf
Detecting Causal Relationships in Distributed Computations: In Search of the Holy Grail http://www.vs.inf.ethz.ch/publ/papers/holygrail.pdf
Merging OT and CRDT Algorithms: http://hal.inria.fr/docs/00/95/71/67/PDF/main.pdf