To prove recursive formulas, or more precisely formulated, a formula $P$ (with free variable $n$) for all $n \in \N$,
we have can use weak or strong induction.
Weak induction may be a \textit{slightly} misleading term, because it isn't necessarily weaker than strong induction.

This section has been moved to the very start of the theory part, even though many of the topics mentioned have not been covered in the summary yet,
such that all the induction proofs can be covered in the same place.
