reserve a,a1,a2,a3,b,b1,b2,b3,r,s,t,u for Real;
reserve n for Nat;
reserve x0,x,x1,x2,x3,y0,y,y1,y2,y3 for Element of REAL n;
reserve L,L0,L1,L2 for Element of line_of_REAL n;

theorem Th52:
  ex x st x in L
proof
  consider x1,x2 such that
A1: L = Line(x1,x2) by Th51;
  take x1;
  thus thesis by A1,EUCLID_4:9;
end;
