CTAN has a new package: drv

[CTAN Announcements]

This package should reach your local mirror in a day.

Jim Hef{}feron
Saint Michael's College

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The following information was provided by our fellow contributor:

Name of contribution: drv.mp
Version number: 0.93
Author's name: Laurent Méhats
Location on CTAN: /graphics/metapost/contrib/macros/drv
Summary description: derivation trees with MetaPost
License type: lppl

Announcement text: 
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drv.mp is a set of MetaPost macros for typesetting
derivation trees (such as used in sequent calculus, type
inference, programming language semantics...)
NO MetaPost knowledge is needed to use these macros.
----------------------------------------------------------------------

This package is located at 
   http://tug.ctan.org/tex-archive/graphics/metapost/contrib/macros/drv
.  More information is at
   http://tug.ctan.org/pkg/drv
(if the package is new it may take a day for that information to 
appear).  We are supported by the TeX Users Group http://www.tug.org .  
Please join a users group; see http://www.tug.org/usergroups.html .