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Global VLBI observations of SN1993J with 9 to 14 antennas for up to 18 hours show clearly that the supernova is expanding in a way consistent with being uniform. The radii (HWHM in microarcseconds) of circular Gaussians used in model fits to the visibility data, together with the observing wavelengths and epochs are: $57\pm4$ (1.3cm, Apr. 26), $91^{+17}_{-10}$ (1.3cm, May 16), $82\pm7$ (3.6cm, May 16), $165^{+8}_{-17}$ (2cm, Jun. 26), $161^{+5}_{-6}$ (3.6cm, Jun. 26). A weighted least-squares linear fit gives an angular expansion velocity of $1.74\pm0.22$ microarcseconds per day and an explosion date of Mar. $27.0\pm3.5$ UT, the latter in agreement with results from optical data. A power-law fit constrained to go through a more precise optical zero point of Mar. 28.0 (Traummell et al., 93 ApJL 414, L21) gives an exponent of $0.97\pm0.04$. Early optical spectra, e.g. measured with the INT on La Palma and the DDO near Toronto, indicate maximum expansion velocities of $17,500\pm500$~km/s (measured at the blue edge of the H$\alpha$ absorption trough). With the assumptions that a) the transverse velocity of the radio emitting region is $10\pm15\%$ larger than the above optical velocity and that b) the brightness distribution of the supernova can be approximated by any model between a uniform disk and a very thin shell, we obtain a distance to M81 of $4.3\pm0.8$ Mpc. All uncertainties are 1 standard deviations. We have continued the observations in intervals of about 6 weeks and should later be able to obtain detailed images of the supernova.
