Question: question on syntax of old Maple code.

I am translating old Maple code to run on Maple 2021.2. This code from 1985. I think it was Maple 3 then. I'll put a link to the paper and page number.

It uses this syntax

Btw, the " above is meant to be % in new Maple. I do not know what w='@W' is supposed to translate to.

The paper is

A DISCUSSION AND IMPLEMENTATION OF KOVACICS ALGORITHM FOR ORDINARY DIFFERENTIAL EQUATIONS

by  Carolyn J. Smith.

Here is the link

https://cs.uwaterloo.ca/research/tr/1984/CS-84-35.pdf

The above is at page 67. Near the end.  The code also uses some old functions, which are not given in the listing, I searched but could not find these.. One is called Lsolve (to solve linear equations, but I can replace this with solve) and  on page 77 it uses these 

           Functions required: scanmap, expcontract, lncontract, explnsimp

These are not given in the source code in the paper. I assume these are old Maple function which no longer exist?. But I can just use simplify for now in their place.

My question is on the use of `@W` and what it could mean? This syntax @ is used in many places in this old Maple code.