You've got the right general idea but the difference between `s` and `t` is not for nesting - you can write a composition operator for a "simple" lens where s=t

You've got the right general idea but the difference between `s` and `t` is not for nesting - you can write a composition operator for a "simple" lens where s=t and a=b. `b` and `t` are just for type-changing updates, like when you replace a field in a tuple or every element in a list.