The 'S' flag indicates that the symbol used for logical negation is ~.
The 'N' flag indicates that the convention that 1 (not 0) is the smallest natural number is maintained throughout.
Here are portable document format copies:
version 3.1S
version 3.1N
version 3.1SN
In an attempt to avoid confusion, these alternate versions can only be purchased in hardcopy from the CreateSpace e-store:
version 3.1S
version 3.1N
version 3.1SN
Like GIAM itself, these alternate versions are licensed under the GNU Free Documentation License version 1.3