157. In the case of many verbs the verb stem is different from the present stem.
Examples:
(1) The verb stem of κηρύσσω is not κηρυσσ- but κηρυκ-. From κηρυκ- the future κηρύξω is formed by the rule given in §156.
(2) The verb stem of βαπτίζω is not βαπτιζ- but βαπτιδ-. From βαπτιδ- the future βαπτίσω is formed by the rule given in §156.