_R_e_v_e_r_s_e _a _V_e_c_t_o_r'_s _E_l_e_m_e_n_t_s
	
	     rev(x)
	
	_D_e_s_c_r_i_p_t_i_o_n:
	
	     rev provides a reversed version of its argument.  It
	     can be used in combination with sort to obtain vectors
	     sorted into descending order.
	
	_E_x_a_m_p_l_e_s:
	
	     # sort into descending order
	     rev(sort(x))