  Recent experiments on Sr_2RuO_4 have indicated the presence of linear nodes
in the superconducting order parameter. Among the possible spin triplet states,
2D p-wave superconductivity with E_u symmetry appears to be inconsistent with
the experiments, whereas the 2D f-wave order parameter with B_1g x E_u symmetry
turns out to be a more likely candidate. Here it is shown how the
quasi-particle bound state wave functions around a single impurity provide a
clear signature of the symmetry of the underlying superconducting order
parameter.
