 Complete the following phrase:  The flexible defence line is not intended to constitute an impenetrable barrier, just close roads passable by vehicles, in order to making the movement of tanks and trucks impossible. For this purpose all of roads in the intermediate woodlands, swamps and mountainous zones has been demolished or blockaded as irreversibly as possible. Hostile infantry rarely cavalry too easily passes through but without resupply they quickly run out of material. After this a small rapid pursuing unit is able to defeat attacker forces unit even up to a regiment size. These skier, riding, cycling or motorcycling mobile forces have strength of a company or less, and use only light arms. The Finnish and Hungarian border guards were able to 