From Max Klein:
 attached is a simulation of the difference dbar - ubar
 using 40pb-1 of ep and 20pb-1 of eD data to determine
 F2(p) and F2(N) which allows to test the sea symmetry.
 Outer error: total, inner statistics.
 The data points are positioned at MRSH (zero difference).
 MRS changed the fit when the NuTeV measurement came, the blue
 line is MRST (PDFLIB code 3,75). The measurement requires
 precision. I have calculated th edifference bt
 one may also take the ratio where things cancel.
 The suggested difference is small (yet may be larger, who knows)
 and in addition shadowing effects are to be controlled.
 Mark Strikhman claims that diffraction allows to
 get this to 2% (see THERA book article, e.g.).
 Such an accuracy should be reachable
 in this measurement with a tuned apparatus.

 I can still improve the picture tomorrow or
 during Cracow but find it not bad for this moment...

 I have not done s-c but that i did 15 years ago, see
 HERA 97 vol1, p99. 1/3(s-c) is the difference of 5/18W2 (cc)
 and F2N. Perhaps the sea quark picture is enough an
 illustration that deuterons are needed for unfolding
 the quarks. note that its not just ubar-dbar, thequestion
 is also what the strange (and charm) contributions are,
 i notice that the PDFs are not unfolded at HERA,
 a programme rather overlooked so far, or impossible
 to study.