trial_by_combat_shown_and_not_invalid_trigger

trial_by_combat_shown_and_not_invalid_trigger = {
	# Scope:puppet_or_actor must be able to fight personally.
	scope:puppet_or_actor = { can_start_single_combat_trigger = yes }
	# Scope:puppet_or_actor cannot challenge someone they have a ceasefire against.
	scope:puppet_or_actor = {
		NOT = { has_truce = scope:recipient }
	}
	# Scope:puppet_or_actor *definitely* cannot challenge someone they're at war with.
	scope:puppet_or_actor = {
		NOT = { is_at_war_with = scope:recipient }
	}
}

As written in game/common/scripted_triggers/01_fp1_scripted_triggers.txt.