if, whether
Very common
Conjunction
Type:Subordinating
Subtype:Conditional
Mood:Indicative preferred
Punctuation:A comma is often used before jestli when it starts a subordinate clause.
Examples
I do not know whether he will come.
Tell me if you have time.
I will ask whether he is at home.
I do not know if I understand it.
Call if you need help.