sentence: a 2d lattice gives an irregular honeycomb tessellation , with equal hexagons with point symmetry ; in the case of a regular triangular lattice it is regular ; in the case of a rectangular lattice the hexagons reduce to rectangles in rows and columns ; a square lattice gives the regular tessellation of squares ; note that the rectangles and the squares can also be generated by other lattices ( for example the lattice defined by the vectors ( 1,0 ) and ( 1/2 ,1 / 2 ) gives squares ) .