The refuge model

This lab is from A-Level and IB, and it is not in the NEET syllabus. A pest has a recessive resistance allele with frequency $q$. You will write one generation of selection and then count the generations until the allele reaches a frequency of $0.5$, with and without a refuge.

The idea. With a refuge of a share $r$ of the area, the effective loss of fitness is $s(1 - r)$. For an effective loss $s_e$, the mean fitness is $1 - s_e(1 - q^2)$, and the new frequency is $\dfrac{q^2 + q(1-q)(1-s_e)}{\text{mean fitness}}$.

Your tasks.

1. Finish next_q. It gives the frequency after one generation of selection with the effective loss s_eff.
2. Finish generations. It gives the number of generations until q reaches $0.5$, for a refuge of the share refuge.
3. Finish slows_down. It gives True if the refuge makes the resistance take more generations than no refuge.