  The Lagrange and Markov spectra have been studied since late 19th century,
concerning badly approximable real numbers. The Mordell-Gruber spectrum has
been studied since 1936, concerning the supremum of the area of a rectangle
centered at the origin that contains no other points of a unimodular lattice.
We develop techniques that incorporate unimodular lattices and integer
sequences, providing the log-systole function which unifies four famous
spectra. We compute the Mordell-Gruber spectrum in the two-dimensional case and
generalize Perron's formulas behind some famous spectra. Furthermore, we
generalize the sum of Cantor sets to prove that certain functions on cartesian
product of two Cantor sets contain an interval. Combining the techniques, we
prove closedness and existence of Hall's interval in several different
applications.
