In mathematics, Hanner's inequalities are results in the theory of Lp spaces. Their proof was published in 1956 by Olof Hanner. They provide a simpler way of proving the uniform convexity of Lp spaces for p ∈ (1, +∞) than the approach proposed by James A. Clarkson in 1936.

Statement of the inequalities

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Let fg ∈ Lp(E), where E is any measure space. If p ∈ [1, 2], then

 

The substitutions F = f + g and G = f − g yield the second of Hanner's inequalities:

 

For p ∈ [2, +∞) the inequalities are reversed (they remain non-strict).

Note that for   the inequalities become equalities which are both the parallelogram rule.

References

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  • Clarkson, James A. (1936). "Uniformly convex spaces". Trans. Amer. Math. Soc. 40 (3). American Mathematical Society: 396–414. doi:10.2307/1989630. JSTOR 1989630. MR1501880
  • Hanner, Olof (1956). "On the uniform convexity of Lp and p". Ark. Mat. 3 (3): 239–244. doi:10.1007/BF02589410. MR0077087