public Process exec(String command, String[] envp) { return null; }
                public Process exec(String command, String[] envp, File file) { return null; }
                public Process exec(String command, List<?> envp, File file) { return null; }
                public Process exec(String[] command) { return null; }
                public Process exec(String[] command, String[] envp) { return null; }

// When the sequence is over, next returns the zero V and false.
// It is valid to call next after reaching the end of the sequence
// or after calling stop. These calls will continue
// to return the zero V and false.
//
// Stop ends the iteration. It must be called when the caller is
// no longer interested in next values and next has not yet
// signaled that the sequence is over (with a false boolean return).

// the caller becomes the goroutine blocked in c, and the goroutine
// formerly blocked in c starts running.
// These switches continue until a call to coroexit(c),
// which ends the use of the coro by releasing the blocked
// goroutine in c and exiting the current goroutine.
//
// Coros are heap allocated and garbage collected, so that user code