 reserve n,m,i,p for Nat,
         h,k,r,r1,r2,x,x0,x1,x2,x3 for Real;
 reserve f,f1,f2,g for Function of REAL,REAL;

theorem
  x0>0 & x1>0 implies [!ln,x0,x1!] = (ln.(x0/x1))/(x0-x1) by Th4;
