... rank condition is equivalent to A, A, * 0. When &, = 0, the rank condition is equivalent to h,X,{X,c$ + /?2,X2u:> * 0. When &, = 0, the rank condition is equivalent to A, X 2 ... observationally equivalent.2 Given that we will focus only on the first and second moments, we may formally state the conditions for two structures to be observationally equivalent in the ... 3.2.1 Two structures S = (B, r, 2) and S = (B, r, 2) are observationally equivalent if and only if the following equivalent conditions hold: (i) B-IT= B- ‘r and B- ‘EB- 1’ = jj- ‘EB- 1’....