2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36113An internal singularity of a string four-dimensional black hole with second order curvature corrections is discussed. A restriction to a minimal size of a neutral black hole is obtained in the frame of the model considered. Vacuum polarization of the surrounding space-time caused by this minimal-size black hole is also discussed.17 pages, 7 Postscript figures, uses mprocl.sty and epsf.sty. Talk given at the "Discussion Meeting on Physics of Black Holes", Bangalore, India, December 8-10, 1997General Relativity and Quantum Cosmologytext