Subpattern restrictions - to appear - until then, see 

Ole Lehrmann Madsen: Building Safe Concurrency Abstractions. Published in

Concurrent Objects and Beyond - Papers dedicated to Akinori Yonezawa on the Occasion of His 65th Birthday

Editors: Gul AghaAtsushi IgarashiNaoki KobayashiHidehiko MasuharaSatoshi Matsuoka,Etsuya ShibayamaKenjiro Taura

Lecture Notes in Computer Science, Volume 8665 2014, ISBN: 978-3-662-44470-2 (Print) 978-3-662-44471-9 (Online)