_C_h_a_n_g_e _t_h_e _P_r_i_n_t _M_o_d_e _t_o _I_n_v_i_s_i_b_l_e
	
	     invisible(expr)
	
	_V_a_l_u_e:
	
	     This function returns a (temporarily) invisible copy of
	     its argument.  This can be useful when it is desired to
	     have functions return values which can be assigned, but
	     which do not print when they are not assigned.
	
	_E_x_a_m_p_l_e_s:
	
	     # These functions both return their argument
	     # The value returned by the second does not print
	     f1 <- function(x) x
	     f2 <- function(x) invisible(x)