The author of this study was born in 1938, studied
mathematics, physics, and astronomy at
the university of Utrecht from 1960
to 1969, and was a teacher of
mathematics from 1970 to 2001 at the Gymnasium Celeanum in Zwolle. After having
steeped oneself in the fields of history of mathematics, history, and
chronology, he became fascinated by the computus paschalis, i.e. the science
developed since the beginning of the third century on behalf of the
determination of the date of Easter Sunday. In 2009 he succeeded in determining
the initial year AD 271 of *De ratione
paschali*, i.e. the medieval Latin text containing the Paschal tract of the
famous third century Alexandrian computist Anatolius. He did it by
reconstructing the proto-Alexandrian 19-year lunar cycle defined to be the
Metonic 19-year lunar cycle necessarily used by Anatolius to construct his
legendary 19-year Paschal cycle. The reconstruction in question was the subject
of his contribution to the international conference on the science of computus
which took place at the university of Galway in 2010. It was published in 2017
as an article in the proceedings of that conference under the title “The
initial year of *De ratione paschali*
and the relevance of its paschal dates”. In the meantime (from 2001 to 2018) he
kept up a sextilingual website (named millennium) on chronology.

This new study developed from the presentation he gave at the
university of Galway in June 2018 under the title “Reconstructing the
Alexandrian 19-year lunar cycles”. Because the paper in question was accepted
outside the theme of the conference, it should not be included as an article in
the proceedings of the conference. Therefore the author, convinced of the
relevance of his recent discoveries, decided, in view of his old age and in
order to lose no time, to publish these new results on his own in the form of
this book, however not without dedicating it to his great teacher and friend
Professor Daniel P. Mc Carthy, who, always attentive, went on critically
following the development of his ideas during the last ten years, and
expressing his gratitude to his beloved wife Marie Luijters for her
unconditional patience with his new ambition.