Let c be the cardinality of the continuum.
We give a family of pairwise incomparable clones (on a countable base set)
2^c members, all with the same unary fragment, namely the set of all unary
operations.
We also give, for each n, a family of 2^c clones all with the same n-ary
fragment, and all containing the set of all unary operations.
We continue our investigation on pcf with weak form of choice.
Characteristically we assume DC + P(Y) when looking and prod_{s in Y} delta_s.
We get more parallel of theorems on pcf.
We prove in ZF that there is an inner product space, in fact, nicely
definable with no orthonormal basis.
We consider the random graph M^n_{\bar{p}} on the set [n], were the
probability of {x,y} being an edge is p_{|x-y|}, and \bar{p}=(p_1,p_2,p_3,...)
is a series of probabilities. We consider the set of all \bar{q} derived from
\bar{p} by inserting 0 probabilities to \bar{p}, or alternatively by decreasing
some of the p_i. We say that \bar{p} hereditarily satisfies the 0-1 law if the
0-1 law (for first order logic) holds in M^n_{\bar{q}} for any \bar{q} derived
from \bar{p} in the relevant way described above.
The \emph{stationary set splitting game} is a game of perfect information of
length $\omega_{1}$ between two players, \unspls and \spl, in which \unspls
chooses stationarily many countable ordinals and \spls tries to continuously
divide them into two stationary pieces. We show that it is possible in ZFC to
force a winning strategy for either player, or for neither.
We deal with relatives of GCH which are provable. In particular we deal with
rank version of the revised GCH. Our motivation was to find such results when
only weak versions of the axiom of choice are assumed but some of the results
gives us additional information even in ZFC.
Our main theorem is about iterated forcing for making the continuum larger
than aleph_2. We present a generalization of math.LO/0303294 which is dealing
with oracles for random, etc., replacing aleph_1, aleph_2 by lambda,lambda^+
(starting with lambda=lambda^{<lambda}>aleph_1). Well, instead of properness we
demand absolute c.c.c. So we get, e.g. the continuum is lambda^+ but we can get
cov(meagre)=lambda. We give some applications.
We prove a strong dichotomy for the number of ultrapowers of a given
countable model associated with nonprincipal ultrafilters on N. They are either
all isomorphic, or else there are $2^{2^{\aleph_0}}$ many nonisomorphic
ultrapowers. We prove the analogous result for metric structures, including
C*-algebras and II$_1$ factors, as well as their relative commutants and
include several applications. We also show that the C*-algebra B(H) always has
nonisomorphic relative commutants in its ultrapowers associated with
nonprincipal ultrafilters on N.
We are interested in examples of a.e.c. with amalgamation having some
(extreme) behaviour concerning types. Note we deal with k being sequence-local,
i.e. local for increasing chains of length a regular cardinal. For any cardinal
theta>= aleph_0 we construct an a.e.c. with amalgamation k with L.S.T.(k) =
theta, |tau_K| = theta such that {kappa : kappa is a regular cardinal and K is
not (2^kappa, kappa)-sequence-local} is maximal. In fact we have a direct
characterization of this class of cardinals: the regular kappa such that there
is no uniform kappa^+-complete ultrafilter.