  Since the discovery of high-Tc LaO_1-xF_xFeAs, and other such systems based
on FeAs layers, several proposals have been made for the superconducting order
parameter Delta_k, on both phenomenological and microscopic grounds. Here we
discuss how the symmetry of Delta_k in the bulk can be determined, assuming
that single crystals will soon be available. We suggest that a measurement of
the dependence of the low temperature specific heat on the angle of a magnetic
field in the FeAs plane is the simplest such method, and calculate
representative specific heat vs. field angle oscillations for the various
candidate states, using a phenomenological band structure fitted to the DFT
Fermi surface.
