https://www.glc.us.es/~jalonso/calculemus/si-r-es-un-reticulo-tal-que-x-%e2%8a%94-y-%e2%8a%93-z-x-%e2%8a%94-y-%e2%8a%93-x-%e2%8a%94-z-entonces-a-%e2%8a%93-b-%e2%8a%94-c-a-%e2%8a%94-c-%e2%8a%93-b-%e2%8a%94-c/