Глобальная конформная калибровка в теории струн

Existence of the conformal gauge for two-dimensional Lorentzian metric is known locally for a long time. We prove that if a Lorentzian metric is given on a plain then the conformal gauge exists on the whole R2. Moreover, we prove the existence of the conformal gauge globally on the whole worldsheets represented by infnite strips with straight boundaries for open and closed bosonic strings.