First cut at documentinf tsearch(3) -- needs work.

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+.\" Copyright (c) 1997 Todd C. Miller <Todd.Miller@courtesan.com>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by Todd C. Miller.
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\"	$OpenBSD: tsearch.3,v 1.1 1997/06/15 23:59:33 millert Exp $
+.\"
+.Dd June 15, 1997
+.Dt TSEARCH 3
+.Os
+.Sh NAME
+.Nm tsearch, tfind, tdelete, twalk
+.Nd manipulate binary search trees
+.Sh SYNOPSIS
+.Fd #include <search.h>
+.Ft void *
+.Fn tdelete "const void *key" "void **rootp", "int (*compar) (const void *, const void *)"
+.Ft void *
+.Fn tfind "const void *key" "void * const *rootp", "int (*compar) (const void *, const void *)"
+.Ft void *
+.Fn tsearch "const void *key" "void **rootp", "int (*compar) (const void *, const void *)"
+.Ft void
+.Fn twalk "const void *root" "void (*compar) (const void *, VISIT, int)"
+.Sh DESCRIPTION
+The
+.Fn tdelete ,
+.Fn tfind ,
+.Fn tsearch ,
+and
+.Fn twalk
+functions manage binary search trees based on algorithms T and D
+from Knuth (6.2.2).  The comparison function passed in by
+the user has the same style of return values as
+.Xr strcmp 3 .
+.Pp
+.Fn Tfind
+searches for the datum matched by the argument
+.Fa key
+in the binary tree rooted at
+.Fa rootp ,
+returning a pointer to the datum if it is found and NULL
+if it is not.
+.Pp
+.Fn Tsearch
+is identical to
+.Fn tfind
+except that if no match is found,
+.Fa key
+is inserted into the tree and a pointer to it is returned.  If
+.Fa rootp
+points to a NULL value a new binary search tree is created.
+.Pp
+.Fn Tdelete
+deletes a node from the specified binary search tree and returns
+a pointer to the parent of the node to be deleted.
+It takes the same arguments as
+.Fn tfind
+and
+.Fn tsearch .
+If the node to be deleted is the root of the binary search tree,
+.Fa rootp
+will be adjusted.
+.Pp
+.Fn Twalk
+walks the binary search tree rooted in
+.fa root
+and calls the function
+.Fa action
+on each node.
+.Fa Action
+is called with three arguments: a pointer to the current node,
+a value from the enum 
+.Sy "typedef enum { preorder, postorder, endorder, leaf } VISIT;"
+specifying the traversal type, and a node level (where level
+zero is the root of the tree).
+.Sh SEE ALSO
+.Xr bsearch 3 ,
+.Xr hsearch 3 ,
+.Xr lsearch 3
+.Sh RETURN VALUES
+The
+.Fn tsearch
+function returns NULL if allocation of a new node fails (usually
+due to a lack of free memory).
+.Pp
+.Fn Tfind ,
+.Fn tsearch ,
+and
+.Fn tdelete
+return NULL if
+.Fa rootp
+is NULL or the datum cannot be found.
+.Pp
+The
+.Fn twalk
+function returns no value.