NOTE No. 2: The Exceptions
Because the Russian language is so easy, it runs the risk of becoming boring to learn. For that reason, the Russians have spiced their language with a few interesting exceptions. Clever as they are, however, the Russian exceptions are based on a rule that you will do well to remember.
Most Russian exceptional verbs have two stems, a present-future stem and a past stem. The present-future stem underlies the present-future tense, the imperative (except for the ава-verbs), and the present participles. The past stem underlies the past tense, the infinitive, and the past participles. The exceptionality of these verbs is that some letter or group of letters is present in one of these stems but not in the other.