Concurrency (understood as message-passing concurrency) is much more expressive than either OO or FP. Milner invented pi-calculus because its predecessor (CCS)

Concurrency (understood as message-passing concurrency) is much more expressive than either OO or FP. Milner invented pi-calculus because its predecessor (CCS) was not expressive enough. One example of the lack of expressivity is that the encoding of Turing machines into CCS is quite awkward, whereas the encoding into pi-calculus is smooth. Still, pi-calculus has expressivity limits, e.g. n-way synchronisation (n > 2) a la Petri nets cannot be encoded in a compositional way, and neither can broadcasting or Ambient-calculus mobility.