can_keep_single_heir_succession_law_trigger

can_keep_single_heir_succession_law_trigger = {
	# The 'can_keep' triggers are dependent on actually having the law. If they aren't, the trigger breakdown for the player breaks and shows incomplete information.
	trigger_if = {
		limit = {
			has_realm_law = single_heir_succession_law
		}
		OR = {
			can_have_single_heir_succession_law_trigger = yes
			# Byzantine Empire / Ceremonial Liege
			historical_succession_access_single_heir_succession_law_trigger = yes
			has_variable = purge_oath_previous_law # ACH Purge Pretenders Oath
		}
	}
}

As written in game/common/scripted_triggers/00_law_triggers.txt.