Marriageable Relations Being Forbidden by Touching

The following statement is from Endless Bliss 4:
"Committing fornication with a woman or touching any part of her with lust, even if by forgetting or by mistake, according to the Hanafi and the Hanbali Madhhabs, causes Hurmat-i musahara [= Marriageable relations being forbidden by touching]." [EB4, pg. 65]

i) What does "touching any part of her with lust, even if by forgetting or by mistake" mean?
ii) Also, if one this occurs, it will become haram for me to marry the woman's [who I touched] mother and her daughters, correct?
iii) Would I be able to marry the woman that I touched with lust even though I cannot marry her mother or daughters?
iv) I heard that since one could not marry the mother of the woman, then the marrying the woman one touched would also be prohibited. Is this correct?

Wa'alaykum al-salam

The word sibr is defined as 'any relation of a man's wife or of a woman's husband whom it is unlawful to marry; as the father, and brother, and son, and paternal uncle and maternal uncle' [Lane's Lexicon]. The hurma al-musahara (inviolability of the above mentioned relation) refers to the unmarriageable relation between two people.

The Hanafi scholars mention that touching a member of the opposite sex establishes such a relation with the touched persons ancestors and descendants if the touch was accompanied by desire during the touching itself. The touching must been direct skin-to-skin contact, without a barrier (unless the barrier was so thin that it does not prevent feeling body heat)..

Desire here is defined as an erection or an increase in erection if the
penis was already erect, with respect to the man.

With respect to the woman, very aged men, and those who do get erections, it consists in a very strong inclination of the heart such that it clouds one's thoughts. [al-Hadiyya al-'Ala'iyya, 352]. This desire has to be present at the moment of contact and is legally inconsequential if it occurs thereafter.

The woman that one actually touched however is still permissible to marry, the only forbidden relation being her descendants (daughters, granddaughters etc) and ancestors (mother, grandmother etc).

As can be seen this is not something that occurs by mistake very easily so it should not lead to situations where one refuses to kiss one's paternal aunt goodbye, for example, out of fear that perhaps one might feel desire. That is just waswasa (baseless misgivings). However, it does mean that some degree of care should be taken when around one's mother or father-in-law and contact should be proper and restrained.

And Allah knows best.
Sohail Hanif, and Faraz Rabbani.