  It is solved the problem on constructed of separately continuous functions on
product of two topological spaces with given restriction. In particular, it is
shown that for every topological space $X$ and first Baire class function
$g:X\to \bf R$ there exists separately continuous function $f:X\times X \to \bf
R$ such that $f(x,x)=g(x)$ for every $x\in X$.
