“…A particular challenge is to determine what special properties
have among all pro‐
groups; so far only a few properties have been found (cf., for example[
2, 15, 29, 35] and references therein). A pro‐
group
is called
‐quadratic (or simply quadratic) if the graded algebra
, endowed with the cup product and with
as a trivial
‐module, is a quadratic algebra over
, that is, all its elements of positive degree are combinations of products of elements of degree 1, and its defining relations are homogeneous relations of degree 2 (see [
34]). A pro‐
group
is called a Bloch–Kato pro‐
group if every closed subgroup
of
is quadratic (see [
32]).…”