Note: in the following, parentheses denote "subscript". "G" denotes "gamma". A round, uncharged current loop is at rest in the xz plane of IRF K. The loop is centered on the Origin. Negative charge circulates around the loop, positive charge remains at rest. There is a nonzero B(y) field at points on the y axis. Viewed from IRF K’, at time t'=0 dB(y)’/dt’=0 at points on the y’ axis. Yet E(z)’=GvB(y) (where G stands for “gamma”). Since the net charge is zero in K’ (as it is in K), and since dB(y)’/dt’=0 at points on the y’axis, what explains the nonzero E(z)’?