for N being Nat
for F being sequence of (TOP-REAL N)
for x being Point of (TOP-REAL N)
for x9 being Point of (Euclid N) st x = x9 holds
( x is_a_cluster_point_of F iff for r being Real
for n being Nat st r > 0 holds
ex m being Nat st
( n <= m & F . m in Ball (x9,r) ) )