  Let $X$ be a simply connected rational elliptic space of formal dimension $n$
and let $\E(X)$ denote the group of homotopy classes of self-equivalences of
$X$. If $X^{[k]}$ denotes the $k^{\text{th}}$ Postikov section of $X$ and
$X^{k}$ denotes its $k^{\text{th}}$ skeleton, then making use of the models of
Sullivan and Quillen we prove that $\E(X)\cong\E(X^{[n]})$ and if
$n>m=max\big\{k \,| \,\pi_{k}(X)\neq 0\big\}$ and $\E(X)$ is finite, then
$\E(X)\cong\E(X^{m+1})$. Moreover, in case when $X$ is 2-connected, we show
that if $\pi_{n}(X)\neq0$, then the group $\E(X)$ is infinite.

Algebraic Topology