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 Th51:
  ex x1,x2 st L = Line(x1,x2)
proof
  L in line_of_REAL n;
  then consider x1,x2 being Element of REAL n such that
A1: L = Line(x1,x2);
  take x1, x2;
  thus thesis by A1;
end;
