How do I fix the Calculus.jl module

New to Julia
2

There a two questions here:

  1. github and Pkg workflow: you will find many discussions on the forum, eg this one, and also general introductions to git online,

  2. regarding this particular problem: you could use T for the element type as a quick fix, but this may fail if finite_difference! widens. Then it would need to calculate the type. I have written

for this purpose, but the calculation is simple.