declare
fun {p1 L}
   case L
   of nil then nil
   [] X|Xs then
      if X=='ping' then
     {Delay 500}
     {Browse 'pong'}
     1|{p1 Xs}
      end
      if X=='pong' then
     {Delay 500}
     {Browse 'ping'}
     'ping'|{p1 Xs}
      end
   end
end

declare
fun {p2 L}
   case L
   of nil then nil
   [] X|Xs then
      if X=='ping' then
     {Delay 500}
     {Browse 'pong'}
     'pong'|{p2 Xs}
      end
      if X=='pong' then
     {Delay 500}
     {Browse 'ping'}
     'ping'|{p2 Xs}
      end
   end
end





declare
proc {gme p1 p2}
   {p1 thread {p2 'ping'} end}
   %{p2 thread {p1} end}
end