  There has for longer been an interest in finding equivalent conditions which
define inner product spaces, and the respective literature is considerable, see
for instance Amir, which lists 350 such results. Here, in this tradition, an
alternative definition of orthogonality is presented which does not make use of
any inner product. This definition, in the spirit of the recently developed
non-wellfounded set theory, is self-referential, or circulatory.
