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 Th48:
  x1 in L & x2 in L implies Line(x1,x2) c= L
proof
  L in line_of_REAL n;
  then ex y1,y2 being Element of REAL n st L = Line(y1,y2);
  hence thesis by EUCLID_4:10;
end;
