A few years ago, Ettore Picutti wrote a very readable paper on Leonardo,
in which he addresses most of the topics your friend seems to be
interested in. Picutti's essay was published in a special issue of
_Investigacion y Ciencia_ (Spanish version of _Scientific American_),
"Temas 1: Grandes Matematicos", pp 6-17, 1995 (ISSN: 1135-5662).
[ Cf. also Picutti, Ettore: "Leonardo Pisano", _Le Scienze_, no 164, 1982;
_Le Scienze, Quaderni_, pp 30-39, 1984. ]
I have read many "Biographies" on Leonardo, but most of them merely are
recycled text on recycled paper or 'softpaper' (= online text).
Let me be naughty for a while if you don't mind... (And, sorry if you do
mind!):
** Example 1.
[ Leonardo Pisano Fibonacci: The Book of Squares, An Annotated Translation
into Modern English By L.E. Sigler, Academic Press, Inc., 1987 ]
What follows is quotation from the "Introduction: A Brief Biography of
Leonardo Pisano (Fibonacci) [1170-post 1240]" of the referred book
(pages xv-xvi):
"Leonardo Pisano was born in 1170 in the city-state of Pisa
in the province of Tuscany in what is now the state of Italy."
Question: Which is the primary source that allegedly proves that Leonardo
was born in 1170 (and not, for instance, in 1171)?
"His father's name was Guilielmo and Leonardo also identified
himself as a descendant of Bonaccio, most probably a not far
removed progenitor. This reference to a famous ancestor was
then a common practice in Italy. In 1225, in his book _Flos_,
Leonardo refers to himself as Leonardo Pisano Bigollo..."
Not quite. Leonardo refers to himself as "Leonardi bigolli pisani" (and
not the other way round!).
Besides... Am I mistaken to say that 1225 is nowhere given in the ms
of _Flos_ (= Flower)? ... Yes... I know that Kurt Vogel, in his
well-known article for the DSB, does mention 1225, and that also many
authors repeat this date.
** Example 2.
[ http://www.lib.virginia.edu/science/parshall/fibonacc.html ]
"Leonardo Fibonacci (PORTRAIT - 42K) was born in Pisa, Italy,
around 1170, the son of Guilielmo Bonacci, a secretary of the
Republic of Pisa and responsible, beginning around 1192, for
directing the Pisan trading colony in Bugia, Algeria."
Comments:
* The portrait referred to above is (as D.E. Smith already pointed out
in 1923) a modern engraving, not based on authentic sources! So...
*It is worth quoting (as Picutti remarked) that the use of the sobriquet
"Fibonacci" most probably originated with the famous historian of
mathematics Guillaume Libri, who in a note on page 19 of his second
volume of "Histoire des sciences mathematiques en Italie" (1838) wrote:
"Fibonacci is a shortened form of _filius Bonacci_, contractions which
are widely exemplified in the making of the surnames of Tuscan families".
There is no a hint of evidence that Leonardo of Pisa referred to himself
as Fibonacci nor that was ever named so by his contemporaries".
* DES says that "An ancient document of 1226 has _Leonardo bigollo quondam
Guilielmi_, in which the Latin form _Bonaccius_ does not appear, but in
which the grandfather has this name. Instead of "Guilielmo Bonacci", as
quoted above in the online text, I would prefer to write "Guglielmo
(= William) Bonaccio".
"Some time after 1192, Bonacci brought his son with him to
Bugia. The father intended for Leonardo to become a merchant
and so arranged for his instruction in calculational techniques,
especially those involving the Hindu-Arabic numerals which had
not yet been introduced into Europe."
According to many mss of the XIIth century, this last statement simply is
NOT true!
** Example 3.
[ Leonard of Pisa and the New Mathematics of the Middle Ages, by Joseph
and Frances Gies. Illustrated by Enrico Arno, New York: HarperCollins
Publishers, 1969 ]
And, as Danny Otero pointed out already, this book is "not the most scholarly
of works, but a very nice read nonetheless". Definitely. The style is more
'casual' than "scholar sources", none the less ... See below:
"Leonard Fibonacci was born in the eighth decade of the twelfth
century, no one knows exactly when."
Instead of giving the ringing 1171, they honestly state "no one know
exactly when". Interpretation of certain data (cf Picutti) may lead us
to say that Leonardo was born in Pisa *circa* 1170.
[ Easy steps: *circa* 1170 ---> ca. 1170 ---> c. 1170 ---> 1170 ]
"Biographies were rare in the Middle Ages, even for kings and popes,
portraits even rarer. There are no contemporary pictures of Leonard."
Instead of fanciful pictures/portraits (for kids or TV shows), the problem
is honestly and scholarly solved.
Et cetera.
Let me end this note quoting the ToC of this book:
A Note on Leonard's Name (very poor, JGC)
I The World of Leonard Fibonacci
II Pisa
III The Education of a Mathematician
IV Voyage to Bugia
V Bugia: the Arab World
VI The Mathematician
VII The Fibonacci Sequence
VIII The Emperor
IX Legacy
All this takes the first 100 pages of the book. The rest is an Appendix
in three parts (pp 101-127).
Warmest regards from warm Montevideo,
Julio Gonzalez Cabillon