input: Write a function to debug the given Python code where the function `f1` is defined incorrectly and does not return a value. The function should ensure that `f1` returns the incremented value of `x` and `f2` correctly uses `f1` to compute the square of the incremented value.
  
  assert f2(2)==9
  assert f2(0)==1
  assert f2(-1)==0
  assert f2(10)==121
  assert f2(-5)==4
output: def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) ** 2