# 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 * R*^{m}× R^{n} is a sum of squares of bilinear forms.