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;

theorem
  x1, x2 are_ldependent2 implies x1 = 0*n or x2 = 0*n or x1 // x2 by Lm4;
