On decomposition of a Boolean function into sum of bent functions

It is proved that every Boolean function in $n$ variables of a constant degree $d$, where $d\leq n/2$, $n$ is even, can be represented as the sum of constant number of bent functions in $n$ variables. It is shown that any cubic Boolean function in $8$ variables is the sum of not more than $4$ bent functions in $8$ variables.