  We study in detail the %Shrek algebra $\mS_n$ in the title which is an
algebra obtained from a polynomial algebra $P_n$ in $n$ variables by adding
commuting, {\em left} (but not two-sided) inverses of the canonical generators
of $P_n$. The algebra $\mS_n$ is non-commutative and neither left nor right
Noetherian but the set of its ideals satisfies the a.c.c., and the ideals {\em
commute}. It is proved that the classical Krull dimension of $\mS_n$ is $2n$;
but the weak and the global dimensions of $\mS_n$ are $n$. The prime and
maximal spectra of $\mS_n$ are found, and the simple $\mS_n$-modules are
classified. It is proved that the algebra $\mS_n$ is central, prime, and {\em
catenary}. The set $\mI_n$ of idempotent ideals of $\mS_n$ is found explicitly.
The set $\mI_n$ is a finite distributive lattice and the number of elements in
the set $\mI_n$ is equal to the {\em Dedekind} number $\gd_n$.
