Section SecondIsomorphism.
Variables (gT : finGroupType) (H K : {group gT}).
Hypothesis nKH : H \subset 'N(K).
Hypothesis sHK : H \subset K.
Hypothesis snHG : H <| G.
Hypothesis snKG : K <| G.

Theorem third_isog : (G / H / (K / H)) \isog (G / K).