Classification of nilpotent lie algebras of dimension nine whose maximum abelian ideal is of dimension seven. - G. Tsagas; A. Kobotis; Triadafyllos Koukouvinos (Int. J. Comput. Math., 2000)

Conditions for the normal rectilinear congruences whose focal surfaces are minimal. - D. Alexiou; G. Tsagas; C. Frangakis (Int. J. Comput. Math., 2001)