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B. Aqzzouz, M. El Kadiri

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Infinite dimensional extension of A.P. Calderon's
theorem on positive semidefinite biquadratic forms

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*## (Lobachevskii Journal of Mathematics,

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Vol.10, pp.3-8)

We extend
to the infinite dimensional separable real
Hilbert spaces a theorem of A. P. Calder\`on
which says that, if $m=2$ or $n=2$,
then every positive semidefinite biquadratic
form on ${\bf R}^m\times {\bf R}^n$ is a sum
of squares of bilinear forms.

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