(* Copyright 1991 Digital Equipment Corporation.               *)
(* Distributed only by permission.                             *)
File: README

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Fsub is a Modula-3 [3] implementation of the F<: calculus [1],[2],[4].
This is the "smallest possible" calculus integrating subtyping with 
polymorphism. The type structure consists of type variables, "Top", 
function spaces, bounded quantification, and recursive types. 
The implementation supports type inference ("argument synthesis"), a 
simple modularization mechanism, and the introduction of arbitrary 
notation on-the-fly.

The system can be obtained by anonymous ftp from gatekeeper.pa.dec.com,
in the "DEC" directory. (To unpack, say: "uncompress <dir>.tar.Z" or
"gunzip <dir>.tar.gz" followed by "tar xvf <dir>.tar".) The
distribution includes DECstation/Ultrix (mips.tar.gz) and
Alpha/Digital Unix (alpha.tar.gz) binaries; it can be ported to other
architectures that support Modula-3 by recompilation (unpack the
"src.tar.gz" archive and type "m3make" in the top-level fsub
directory).

The Fsub licence is covered by the Modula-3 licence (included);
there is nothing to sign. If needed, Modula-3 can be obtained by 
anonymous ftp from gatekeeper.pa.dec.com.

A manual "F-sub, the system" is included in postscript format (in
doc.tar.Z). It will print on Apple LaserWriter II and HP LaserJet
postscript printers.

To install Fsub, move the appropriate binary (e.g mips/Fsub)
to some convenient location, and invoke it from your working directory.
There are no shell-line parameters. A local file called
"Startup.fsub", if found, is loaded at startup.

------
[1] L.Cardelli, J.C.Mitchell, S.Martini, A.Scedrov: "An extension
    of system F with subtyping", Proc. TACS'91 & SRC Report #80.
[2] P.-L.Curien, G.Ghelli: "Subyping + extensionaliy: confluence
    of beta-eta reductions in F<=", Proc. TACS'91.
[3] G.Nelson(ed.): Systems Programming in Modula-3. 
    Prentice Hall, ISBN 0-13-590464-1, 1991.
[4] B.C.Pierce: Bounded quantification is undecidable, Proc. POPL'92.
 
