for n being Nat
for A being Subset of (REAL n)
for x, x1, x2, x3 being Element of REAL n st x in plane (x1,x2,x3) & ex c1, c2, c3 being Real st
( (c1 + c2) + c3 = 0 & x = ((c1 * x1) + (c2 * x2)) + (c3 * x3) ) holds
0* n in plane (x1,x2,x3)