is the center of the tree; ai, i= 1, 2,..., m, bj, j= 1, 2,..., n, and ck, k= 1, 2,..., r are the vertices of
the tree adjacent to a0; each ai is the center of a diameter four tree, each bj is the center of a
star, and each ck is a pendant vertex. Here we give graceful labelings to some new classes
of diameter six trees a0; a1, a2,..., am; b1, b2,..., bn; c1, c2,..., cr in which the branches of a
diameter four tree incident on a0 are of same type, ie either they are all odd branches or …