Use Nominative with љсть and Genitive with нљт.
The word љсть 'there is' (not to be confused with the identical sounding infinitive љсть 'to eat') can often be translated by the English verb have: There is a genitive case in French = French has a genitive case.
The uninflected word нљт is a combination of не plus љсть; when it means 'there is no' it requires that the noun be in the Genitive case.
Здљсь љсть студљнты (Nom.) There are students here.
Здљсь нљт студљнтов (Gen.). There are no students here.
Both words can be used alone in short answers:
— Во францџзском языкљ љсть родќтельный падљж? "Is there a genitive case in French?"
— Љсть. "Yes (there is)."
— Нљт. "No (there isn't)."
To indicate the possessor, use у + Genitive case:
— У тебї (Gen.) љсть рџчка? "Do you have a pen?"
— Дђ, у менї (Gen.) љсть рџчка. "Yes I do."
— Нљт, у менї (Gen.) нљт рџчки. "No I don't."
The verb љсть must be omitted, when the emphasis is not on the fact of possession, but on some property of the object. E.g., when you're asked if your sister has blue eyes, the question is not whether she has eyes--the question is about their color:
— У твољй сестрІ голубІе глазђ? "Does your sister have blue eyes?"
— Нет, (не голубІе). "No, they aren't blue."
Sometimes the word or phrase that is the focus of the sentence is also pronounced with additional stress. Obviously, when љсть is stressed, it won't be left out; when it is not, it is usually left out.
— У тебї зђвтра љсть экзђмен? (I know you're in the middle of finals, and I'm wondering if you have one tomorow.) "Do you have a test tomorrow?"
— У тебї зђвтра экзђмен? (I know you have a test, and I'm wondering if it is tomorrow.) "Is your test tomorrow?"
Observe the contrast between the conversations below. In the first one, the question is whether or not the theater has any cheap seats. In the second, the question is whether the theater's seats are cheap. The verb љсть is crucial in the first case, but must be omitted in the second.
— У вђс љсть дешёвые билљты? "Do you have any cheap seats?"
— Дђ, љсть. "Yes, we do."
— У вђс дешёвые билљты? "Are your seats cheap?"
— Дђ, дешёвые. "Yes, they are."
The verb љсть must also be omitted, when the object is a disease or some intangible condition (because it does not indicate possession):
У негћ грип. He has the flu.
У нђс в семьљ большће несчђстье. We have a tragedy in the family.