for r2, x0 being Real for f being PartFunc of REAL,REAL st 0< r2 & ].(x0 - r2),x0.[\/].x0,(x0 + r2).[c=dom f holds for r1, r2 being Real st r1 < x0 & x0 < r2 holds ex g1, g2 being Real st ( r1 < g1 & g1 < x0 & g1 indom f & g2 < r2 & x0 < g2 & g2 indom f )