I think the demonstration is in Hoare's book on co-operating sequential processes, but if you have pure processes and message passing, you can simulate conventional variables. Here's an Erlang version: variable_loop(State) -> receive {ask,Sender} -> Sender!{self(),State}, variable_loop(State) ; {tell,New_State} -> variable_loop(New_State) end. new_variable(Initial_State) -> spawn(fun () -> variable_loop(Initial_State) end). fetch(Variable) -> Variable!{ask,self()}, receive {Variable,State} -> State end. store(Variable, New_State) -> Variable!{tell,New_State}. new_array(Size, Initial_State) -> list_to_tuple([new_variable(Initial_State) || Dummy <- lists:seq(1, Size)]). fetch(Array, Index) -> fetch(element(Index, Array)). store(Array, Index, New_State) -> store(element(Index, Array), New_State). The simulation of (shared) mutable variables and arrays in pure CSP is very similar. This pretty much _has_ to be possible in any language that has concurrent processes that can communicate in some fashion. There are also quite elementary ways to simulate locking. So we can solve any concurrent problem that, say, C++ with Intel's TBB library, or Java with java.util.concurrent, or any other such language can solve. We can even get ourselves just as far into extremely serious trouble as we can using those languages, it's just that we don't _have_ to. -- If stupidity were a crime, who'd 'scape hanging?