An article of John Baez, where results of Hoàng Xuân Sính's thesis are explained in a historical context.
Grothendieck comments in a letter to R. Brown (5.5.82) :
"Also he [Quillen] had a promising approach to higher
K-invariants, which, he told me, was more or less
equivalent to a more computational transcription
of a somewhat abstract definition I had in mind
in terms of "enveloping n-Picard categories"
of a given additive category C, say, whose invariants
pi_i should yield the invariants K^i(C). (The
case n = 1 was worked out by a Vietnamese woman
student of mine around that time, Mme Sinh...)"
In "Récoltes et Semailles", Grothendieck writes :
"Un autre cas assez à part est celui de Mme Sinh,
que j'avais d'abord rencontrée à Hanoi en décembre
1967, à l'occasion d'un cours-séminaire d'un mois
que j'ai donné à l'université évacuée de Hanoi.
Je lui ai proposé l'année suivante son sujet de thèse.
Elle a travaillé dans les conditions particulièrement
difficiles des temps de guerre, son contact avec moi
se bornant à une correspondance épisodique.
Elle a pu venir en France en 1974/75 (à l'occasion
du congrès international de mathématiciens à
Vancouver), et passer alors sa thèse à Paris (devant
un jury présidé par Cartan, et comprenant de plus
Schwartz, Deny, Zisman et moi)."
Sinh's approach is also mentioned in a letter
of Grothendieck to Knudsen of 1973, see here, p. 41.
A subtle problem with traces and determinants in triangulated categories
has originally been discovered by Daniel Ferrand; cf. arxiv.
Determinant functors appear in this article of Knudsen and Mumford of 1975, see here, p. 23.
Cf. also P. Deligne, "Le déterminant de la cohomologie", §4,
in: Current trends in arithmetical algebraic geometry
(Arcata, Calif., 1985), AMS Contemp. Math. 67, p. 93-177, 1987.
Grothendieck reports on his stay in Vietnam, Dec. 1967: scans (pdf).
According to the web page of Thang Long University,
Mrs Hoàng Xuân Sính remembers two main impressions from her contacts with A. Grothendieck:
(1) A good teacher is a teacher who turns something difficult into something easy.
(2) We should always avoid anything that is fictitious, live in accordance to our own feelings and value simple people.
Illusie relates the following (Notices AMS, Oct. 2010, p. 1111 f.).
"Once, Grothendieck told me, it must have been in 1969:
«We have the K-groups defined by vector bundles,
but we could take vector bundles with a filtration of
length one (with quotient a vector bundle), vector bundles
with filtrations of length 2, length n, with associated
graded still vector bundles... Then you have operations
such as forgetting a step of the filtration, or taking
a quotient by one step. This way you get some simplicial
structure, which should deserve to be studied and
could yield interesting homotopy invariants.»"
