theorem Th68: :: TOPGEN_5:68

for p being Point of (TOP-REAL 2) st p `2 >= 0 holds
for x, a being Real
for r being positive Real st 0 < (+ (x,r)) . p & (+ (x,r)) . p < a & a <= 1 holds
p in Ball (|[x,(r * a)]|,(r * a))