B. Aqzzouz
M. El Kadiri

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

(Lobachevskii Journal of Mathematics, Volume X)

We extend to the infinite dimensional separable real Hilbert spaces a theorem of A. P. Calderòn which says that, if m=2 or n=2, then every positive semidefinite biquadratic form on Rm× Rn is a sum of squares of bilinear forms.
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