Diagonals of a rhombus
Type
Text[ProveDetails[ArePerpendicular[k,l]]]
to see that the diagonals of the rhombus are indeed perpendicular, at least "on parts". (This can also be achieved by using the Relation tool by comparing k and l.) Try also Text[ProveDetails[AreParallel[k,l]]] to learn the "other part" of the truth.