Eiruvin 34a, b

The rabbis debate with each other about placing an eiruv on a reed.  Is the eiruv prohibited on Shabbat? on Festivals?  Considerations worthy of debate include the timing of the placement, the softness of the reed, whether or not the reed has been displaced and then reestablished in the ground, the depth or height of the placement... and more.

They also look at placing an eiruv in or on a cupboard.  Depending on the height of the cupboard, whether or not it has a window through which a rope can be placed, whether or not the cupboard can be tilted, and other factors, the eiruv may or may not be prohibited.

The rabbis seem to generate examples to allow better understanding of the nuances of their rulings.  What I glean from this daf alone:

• Intention is not enough; a deed must be completed to be permissible
• If a Festival occurs immediately before Shabbat, the eiruv must be established before the Festival because placement should not be thought to be allowed just before Shabbat
• An eiruv placed in the public domain on a wall below10 handbreadths is valid
• An eiruv in the same circumstance placed above 10 handbreadths is not a valid eiruv because it is in a public domain while the person's residence is in a private domain
• An eiruv placed on top of a cupboard in a private domain, above 10 handbreadths, is a valid eiruv
• An eiruv in the same circumstance placed below 10 handbreadths is not a valid eiruv because the that area is a karmelit and the eruv cannot be transferred to his private domain on Shabbat
• If the cupboard can be tilted to the right height, the eiruv will be valid
• If the top of the cupboard projects beyond 4 cubits, ie. beyond the private domain/Shabbat residence, this can still be allowed if carrying happens in increments  within the 4 cubit range (R Yehuda HaNasi)
• An eiruv is valid when placed in this tall cupboard where the cupboard has a window -- a rope is used to wind through the window to create the eiruv
• A pit in the private domain can hold a valid eiruv because the private domain extends up to the sky and thus down into the ground
• To establish one's Shabbat residence, the eiruv must be placed in the same domain as the person's primary residence 
• A rabbinic decree or a shevut does not apply during twilight
• One must be able to retrieve one's eiruv during Shabbat (not crossing from one domain to another) 
• If an eiruv is placed on a reed/pole that becomes detatched from the ground and then stuck back into the ground, the eiruv is valid 
• At first the rabbis thought that the determining factor for use of reeds was the hardness/softness of the reed
• Certain species are considered to be food crops in a vineyard and thus prohibited
• Other species are considered to be types of trees and thus they are not food crops in a vineyard and may be used to hold an eiruv on Shabbat 

This is what I read tonight.
I am sure that I have misread and misunderstood different pieces, and this was a relatively uncomplicated daf.

It continues to boggle my mind when I think about how much I don't know.