“…The dual weighted residual (DWR) method promoted by Becker and Rannacher [5], see also [3,7,22,24,33], the general framework by Prodhumme and Oden [36,40], the approach of Maday and Patera [31], multi-objective error estimation in [16,23,46], enhanced least-squares finite element methods by Chaudhry et al [8], or the constitutive relation error (CRE) approach of Ladevèze et al [28,30] and Rey et al [42][43][44], see also the references therein, are very popular approaches to goal-oriented error estimation; this can also be built in the discretization scheme as in Kergrene et al [27]. The obtained bounds are, however, often not guaranteed in the sense of yielding a fully computable number that is rigorously greater than or equal to the goal error.…”