STACK

$A_1|Ax_1\ I\ A_2|Ax_2\ --\$
$S_1\ I\ S_2\ --\$

DESCRIPTION

Red book operator replaces a subsequence of the elements of
the first operand by the entire contents of the third operand.
The subsequence that is replaced begins at index I in the first operand;
its length is the same as the length of the third operand.
The objects are copied from the third operand to the first,
as if by a sequence of individual get and put operations.

ORIGIN

Core code registered in systemdict.