theorem Th1: :: TOPALG_5:1

for a, r, s being Real st r <= s holds
for p being Point of (Closed-Interval-MSpace (r,s)) holds
( Ball (p,a) = [.r,s.] or Ball (p,a) = [.r,(p + a).[ or Ball (p,a) = ].(p - a),s.] or Ball (p,a) = ].(p - a),(p + a).[ )