# The most specific common parent between `self` and `other`
	# Return null if the two node are unrelated (distinct root)
	fun common_parent(other: ANode): nullable ANode
	do
		# First, get the same depth
		var s: nullable ANode = self
		var o: nullable ANode = other
		var d = s.depth - o.depth
		while d > 0 do
			s = s.parent
			d -= 1
		end
		while d < 0 do
			o = o.parent
			d += 1
		end
		assert o.depth == s.depth
		# Second, go up until same in found
		while s != o do
			s = s.parent
			o = o.parent
		end
		return s
	end