+int os_string_length (zchar *);
+void os_tick (void);
+zword os_to_true_colour (int);
+int os_wrap_window (int);
+void os_window_height (int, int);
+
+void seed_random (int);
+void restart_screen (void);
+void refresh_text_style (void);
+void call (zword, int, zword *, int);
+void split_window (zword);
+void script_open (void);
+void script_close (void);
+
+//FILE *os_path_open (const char *, const char *, long *);
+
+//zword save_quetzal (FILE *, zbyte *);
+//zword restore_quetzal (FILE *, zbyte *);
+
+void erase_window (zword);
+
+extern void (*op0_opcodes[]) (void);
+extern void (*op1_opcodes[]) (void);
+extern void (*op2_opcodes[]) (void);
+extern void (*var_opcodes[]) (void);
+
+extern zchar* decoded;
+extern zchar* encoded;