inline quat_t operator-( quat_t a, quat_t b ) { return quat_t( a.x - b.x, a.y - b.y, a.z - b.z, a.w - b.w );
inline quat_t quat_t::operator-() { return quat_t( -x, -y, -z, -w );
inline quat_t operator-( quat_t a, quat_t b ) {	return quat_t( a.x - b.x, a.y - b.y, a.z - b.z, a.w - b.w );}