def field_on_space(function_space, arguments):
    """ Returns the corresponding argument if the supplied list of arguments
    contains a field that exists on the specified space. Otherwise
    returns None."""
    if function_space.mangled_name in arguments.unique_fs_names:
        for arg in arguments.args:
            if (arg.type == 'gh_field' and arg.function_space.orig_name ==
                function_space.orig_name):
                return arg
    return None
