tsort with odd number of items does not give an error.

[junkio]

    $ tsort --version
    tsort (coreutils) 4.5.4
    Written by Mark Kettenis.

    Copyright (C) 2002 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The Info page describes:

   `tsort' reads its input as pairs of strings, separated by
   blanks, indicating a partial ordering.  The output is a total
   ordering that corresponds to the given partial ordering.

I am not quite sure what "as pairs of strings" exactly means
when there are more then two tokens on a line.  Does the
following mean "a < b && c < d" (no ordering is specified
between b and c), or "a < b && b < c && c < d"?  What the
implementation does implies the former:

    $ echo a b c d | tsort
    a
    c
    b
    d

However, then what does the following mean?

    $ echo a b c | tsort
    a
    c
    b

It is clear from the output this does not mean "a < b && b < c"
to the implementation.  But it gets worse.

    $ (echo a b c; echo c a) | tsort
    a
    c
    b

The second line explicitly specifies "c < a" but the output does
not honor that.  It appears that the only sane interpretation of
the behaviour of the implementation is that the entire output is
undefined when there is a line with an odd number of items in
the input, and no error diagnosis is made.  I think it should at
least complain about such an input.