What is the relation between Tchu-Len and Chod.

Both they where practized by the Great Yoghi Padampa Sanghie who reached the stage of  Dorje Chan.
 He was contemporary of Milarepa, there is a very nice story of their meeting,He is belived to live up to these days at WuTaiShan China.

Tchulen is the union of relative and absolute Bodhicitta,Tchu is bodhi (light),len is citta the mind,in this context..

Chod is the cutting of all conceptual thought,specially the grasping at a self existent I,or pure intention and action united in the aim of destroying yours and all sentient beings sufferings, the grasping habit to a self existing reality.

How we do that with Tchulen,we take the essence of the union of the two bodhicitta by meditating on the clean clear nature of the mind, embracing the relative and absolute in the clean clear light of our mind nature,destroying naturally all allucinations about you,action and others.

Uniting all into the clean clear light,cutting off naturally with no effort all the rest of concepts.

Just clean clear light is all there is beyond all words and conceptions,checking always,with the fish like awareness, if the grasping to the old habit again reify the old reality, that never existed in the way it appeared.