Left: orbital period of the third companion P₂ versus orbital period of the inner binary P₁ for 222 triple systems within the original Kepler field (Borkovits et al. 2016). Area with the lack of triples is highlighted with yellow. The stability limit is calculated for the parameter s = 1.8 in Eq. (1), with the assumption that m₀ = m₁ = m₂ = 1, for the mean value of orbital eccentricity of the outer orbit ⟨ e₂ ⟩ ≃ 0.35. Right: eccentricity of the outer orbit as a function of the orbital period ratio. Dash-dot line is stability criterion according to Mardling & Aarseth (2001), dashed line (Sterzik & Tokovinin 2002) and red solid line is empirical criterion according to observations of Tokovinin (2007). Eighty-eight triples from Multiple Star Catalog are plotted with black crosses (Tokovinin 1997) and 222 triples in the original Kepler field are plotted with black dots (Borkovits et al. 2016).