  For each odd prime p>=5, there exist finite p-groups G with derived quotient
G/D(G)=C(p)xC(p) and nearly constant transfer kernel type k(G)=(1,2,...,2)
having two fixed points. It is proved that, for p=7, this type k(G) with the
simplest possible case of logarithmic abelian quotient invariants
t(G)=(11111,111,21,21,21,21,21,21) of the eight maximal subgroups is realized
by exactly 98 non-metabelian Schur sigma-groups S of order 7^11 with fixed
derived length dl(S)=3 and metabelianizations S/D(D(S)) of order 7^7. For p=5,
the type k(G) with t(G)=(2111,111,21,21,21,21) leads to infinitely many
non-metabelian Schur sigma-groups S of order at least 5^14 with unbounded
derived length dl(S)>=3 and metabelianizations S/D(D(S)) of fixed order 5^7.
These results admit the conclusion that d=-159592 is the first known
discriminant of an imaginary quadratic field with 7-class field tower of
precise length L=3, and d=-90868 is a discriminant of an imaginary quadratic
field with 5-class field tower of length L>=3, whose exact length remains
unknown.
