[Bug] Hakulinen is false

[lrnv]

This issue simply tracks the fact that the Hakulinen implementation we have does not match what is done in the R package yet. In cause, the rather poor documentation of the method. A few links that might be useful so solve this :

• https://www.mayo.edu/research/documents/tr53pdf/DOC-10027379
• https://www.mayo.edu/research/documents/biostat-63pdf/doc-10027294 with an actually potentially usefull explanation to understand the matter, with a correct notation.
• https://stat.ethz.ch/R-manual/R-devel/library/survival/html/survexp.html for the R implementation in survexp.
• https://sci-hub.se/https://link.springer.com/book/10.1007/978-1-4757-3294-8 section 10.3.4 page 275 (285 of the pdf).