2. 0<n
3.
f:(
(n-1)
), m:(n-1).
3. sum(f(x) | x < n-1) = f(m)+sum(if x=
m
0 else f(x) fi | x < n-1)
4. f :
n
5.
m:(n-1). sum(f(x) | x < n-1) = f(m)+sum(if x=m 0 else f(x) fi | x < n-1)
6. m :
n
7. m = n-1
8.
n = 0
9. n-1 = n-1
sum(f(x) | x < n-1) = sum(if x=n-1 0 else f(x) fi | x < n-1)
sum(f(x) | x < n) = sum(g(x) | x < n)
