Let u and v be two linearly independent vectors that connect the graphene atom "A1" to two of its nearest atoms with the same bond directions. That is, if one numbers consecutive carbons around a graphene cell with C1 to C6, then u can be the vector from C1 to C3, and v be the vector from C1 to C5. Then, for any other atom "A2" with same class as "A1", the vector from "A1" to "A2" can be written as a linear combination "n" u + "m" v, where "n" and "m" are integers. And, conversely, each pair of integers ("n","m") defines a possible position for "A2".