The length of each side of a convex quadrilateral ABCD is a positive integer. If the sum of the lengths of any three sides is divisible by the length of the remaining side then prove that some two sides of the quadrilateral have the same length.
P = d (k1 + 1) = b (k2 + 1) = c (k3 + 1) = a (k4 + 1)
