A survey of stream processing. R Stephens 95 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.52.9500&rep=rep1&type=pdf section 6.1
A mathematical theory of synchronous concurrent algoriths. BC Thompson 87 http://etheses.whiterose.ac.uk/945/1/uk_bl_ethos_379746.pdf