Robs Syms by Rob Knop is a collection of Equates and Macros for use with the Merlin 128 assembler.  Here is the text from the readme file on the disk:

This archive has six files: robsequs.s, robsmacs.s, robsjsr.s, robsequs.asm, robsmacs.asm, and robsjsr.asm. The .s files are Merlin files (readable by the Merlin editor), the first two of which I include in most  everything I write (with Merlin's PUT command). The .asm files are also Merlin code, but converted to a format readable by a normal text editor such as ZED.

They are archived and distributed so that people can understand any other Merlin source that I distribute! :)

Notes on robsequs: this file contains a stack of useful equates. Mostly it is Kernal routines and zero page equates, although a few MMU registers and other random stuff is thrown in. A note about the zero page equates: a glance at the file will show that I am a GEOS programmer at heart. The zero page pseudoregisters are very reminiscent of r0, r1, ... from geosSymbols. These zero page registers are all in zero page space used by BASIC but not by the Kernal. Thus, using these registers is not possible with a ML program that needs to interface with BASIC (unless you are very careful and/or muck around with the MMU register $d507 to move zero page around).

Notes on robsmacs: Macros for use in Merlin. You will notice that most of them are straight out of geosMacros. Yup, I'm a GEOS programmer who grew addicted to the geoProgrammer macros!

Notes on robsjsr: This is a little JSRFAR sort of routine that resides in zero page. It has the advantage over the usual 128 JSRFAR that it returns to the bank from whence it was called (whereas the usual 128 JSRFAR always returns to Bank 15). The comments describe it fairly well, I think.