Adámek, JiríSousa, Lurdes2015-09-152015-09-1520010927-2852http://hdl.handle.net/10400.19/2915For each concrete category (K,U) an extension LIM(K,U) is constructed and under certain ‘smallness conditions’ it is proved that LIM(K,U) is a solid hull of (K,U), i.e., the least finally dense solid extension of (K,U). A full subcategory of Top_2 is presented which does not have a solid hull.engconcrete categoryMacNeille completionsolid hulllimit closurejournal article