References
- GOLDNBERG , R. R . 1976 . Methods of Real Analysis , 2nd edition , 202 New York : John Wiley and Sons .
- TRENCH , W. F . 1978 . Advanced Calculus , 147 New York : Harper and Row .
- BRUCKNER , A. M . 1978 . Diåerentiation of Real Functions, Lecture Notes in Mathematics , 46 – 48 . Berlin : Springer-Verlag .