tensions within exp. data sets; this is something that can be explored on the PDF fitter level, but then can be examined with the experimental groups; as a start, we propose to examine the impacts of the different ttbar observables, for both ATLAS and CMS, on the global PDF fits; results to be presented in the Les Houches writeup

theory uncertainties; both CT and NNPDF are currently carrying out studies; perhaps the Xfitter and MMHT groups can be added; results to be presented in the Les Houches writeup