/* Projects 2 and later. */
SYS_HALT, /* Halt the operating system. */
SYS_EXIT, /* Terminate this process. */
+ SYS_EXEC, /* Start another process. */
SYS_WAIT, /* Wait for a child process to die. */
SYS_CREATE, /* Create a file. */
SYS_REMOVE, /* Delete a file. */