`(SBC) :` Gọi `MN nn SC = I`

`to I in MN subset (AMN) ; I in SC subset (SCD) to I in (AMN) nn (SCD)`

`(ABCD):` Gọi `AN nn CD = J`

`to J in AN subset (AMN) ; J in CD subset (SCD) to J in (AMN) nn (SCD)`

`to IJ = (AMN) nn (SCD)`