If the answer to a question is 'no', you may omit the main verb.
Examples:
Question | Answer | Answer |
Informal, spoken language | Emphatic spoken and formal language | |
Will she come to the party tomorrow? | No, she won't. | No, she will not. |
Has Tom finished the report? | No, he hasn't. | No, he has not. |
Do you study Russian this semester? | No, we don't. | No, we do not. |