Kulsha suggested two ways to deal with elements 121–156, that lack precise analogues among earlier elements. In his first form (2011, after Pyykkö's paper was published), elements 121–138 and 139–156 are placed as two separate rows (together called "ultransition elements"), related by the addition of a 5g subshell into the core, as according to Pyykkö's calculations of oxidation states, they should respectively mimic lanthanides and actinides. In his second suggestion (2016), elements 121–142 form a g-block (as they have 5g activity), while elements 143–156 form an f-block placed under actinium through nobelium.