  Over the years questions have arisen about T-ideals of (noncommutative)
polynomials. But when evaluating a noncentral polynomial in subalgebras of
matrices, one often has little control in determining the specific evaluations
of the polynomial. One way of overcoming this difficulty in characteristic 0,
is to reduce to multilinear polynomials and utilizing the representation theory
of the symmetric group. But this technique is unavailable in characteristic
$p>0$.
  An alternative method, which succeeds, is the process of ``hiking'' a
polynomial, in which one specializes its indeterminates in several stages, to
obtain a polynomial that contains Capelli polynomials, in order to get control
on its evaluations. This method was utilized on homogeneous polynomials in the
proof of Specht's conjecture for affine algebras over fields of positive
characteristic. In this paper we develop hiking further to nonhomogeneous
polynomials, to apply to the representability question. Kemer proved in 1988
that every affine relatively free PI algebra over an infinite field, is
representable. In 2010, the first author of this paper proved more generally
that every affine relatively free PI algebra over any commutative Noetherian
unital ring is representable. We present a different, complete, proof, based on
hiking nonhomogeneous polynomials, over finite fields. We then obtain the full
result over a Noetherian commutative ring, using Noetherian induction on
T-ideals.
  The bulk of the proof is for the case of a base field of positive
characteristic. Here, whereas the usage of hiking is more direct than in
proving Specht's conjecture, one must consider nonhomogeneous polynomials when
the base ring is finite, which entails certain difficulties to be overcome.
  In the appendix we show how hiking can be adapted to prove the involutory
versions, as well as various graded and nonassociative theorems.
