NECESSARY FLEXIBILITY CONDITIONS OF SEMIDISCRETE SURFACES.

In this paper we study necessary conditions of flexibility for
semidiscrete surfaces. For 2-ribbon semidiscrete surfaces we
prove their one-parametric finite flexibility. In particular we
write down a system of differential equations describing flexions
in the case of existence. Further we find infinitesimal criterions
of 3-ribbon flexibility. Finally, we discuss the relation
between general semidiscrete surface flexibility and 3-ribbon
flexibility.