MF109-110: Logical difficulties with the modern theory of limits (Engish)

...we examine an extended harmonic sequence formed by playing the Collatz game (also called the 3n+1 problem...). We will see the essential problem is that the definition actually requires us to make an infinite number of computations to assert that a general `sequence' has a limit.

https://www.youtube.com/watch?v=Ek0URXLCZCE