The State of State Machines
State machines are incompatible with concurrent systems.  For example there is no nondeterministic state machine for the following program:   IndeterminateLargeNumber:[]→Natural ≡
       []↦
          aCounting←Counting.[], // Bind aCounting to a newly created Counting
          aCounting.go|||  // Send aCounting a go message while concurrently
          aCounting.stop   // sending aCounting a stop message

    Counting:[ ]→Interface go→Void, stop→Natural 
       ≡ []  ↦↦   // constructor has no arguments 
          count:=0,   // The variable count is initially 0
          continue:=False|  // The variable continue is initially False
          go ↦      // When a go message is received: 
            continue cases   // Cases for continue are as follows:
                     True then  // If continue is True,  
                        count:=count+1;         // then increment count and afterward
                        Hole (This Counting).go      // in a hole in the region of mutual exclusion,  send a go message this instance of Counting
                     else Void     // If continue is False, then return Void
          stop ↦    // When a stop message is received:
              continue:=False;       // Assign continue the value False and then
              count     // return the value of count

See the following for an explanation:https://papers.ssrn.com/abstract=3459566