не обязательно должен быть
• The laser does not need to be very powerful.
• The coacervating agent need not be a micromolecular substance that can form hydrogen bonds.
• The reactant does not have to be a stereoisomer.
• It is not necessary that the Xk be independent.
• It is not necessary for these liquids to be totally immiscible.
Русско-английский научно-технический словарь