I believe "as" can describe a sense of simultaneous occurrence whereas "when" gives a sense of sequential occurrence.
When I reached the house I saw some guy walk out the back door.
1. You reach the house, action completed. 2. AFTER you reached the house, you saw some guy.
As I reached the house I saw some guy walk out the back door.
1. As you are completing the action of reaching the house you see some guy.
It can also be used to create distance in time (when) vs something in passing (as).
When I was younger, I would unload my friend's truck on the farm since I was stronger.
(in the past)
I saw my friend unloading his truck on the farm, but as I was younger, I told him I'd do it since I was stronger.
(in the present)
But just then, as he reached into his pocket, I saw the bale straps give way.
(simultaneous events)
Example of "when" and "as" in the same scene: He raised the gun to her head to draw further attention to his apparent intent. With her body trembling, all she could think of was at this distance any attempt to escape would be futile. She knew that when he pulls that trigger it would already be too late. He tightens his grip to get ready for the kick but as he pulls the trigger the girl suddenly drops dead. A faint whirr and a glottal stop - the bullet piercing her spinal column - all from a trajectory that can be traced back to a rear window. "There he is!". He rushes to the window "Hey you there! Stop!". The assassin quickly disappears into the night, aided by an already fastened rope the dark figure dances over the adjoining apartment wall. Time to give chase. It's a long, long way down Spunkmeyer. Fortunately when things get this desperate, jumping out of an open window on the fifth floor doesn't seem so crazy. He looks back at his target. Her corpse lay limp on the floor. A growing red stain radiating from the exit wound.
'even when' is used to make explicit an included situation that might be thought of as an exception. So:
- "A soldier must obey all orders, even when he disagrees with them"
- "The accused is entitled to a fair trial, even when he seems obviously guilty"
The sentence you quote admits of two slightly different meaning. Exactly as written, it should mean:
"proving an antitrust violation requires detailed evidence of both causation and intent. This is difficult, regardless of whether a patentee should not be permitted to extend its rights, which you might think would make it easier."
But I believe the intended meaning is:
"proving an antitrust violation requires detailed evidence of both causation and intent, and this is difficult. But it is required, regardless of whether a patentee should not be permitted to extend its rights, which you might think should make it not required."
My personal belief is that a comma after 'difficult' would make it clearer.
Best Answer
The choice really hinges on the durative or punctual aspect of the particular verb (or verb construction, like was sleeping) in the adverbial clause. To illustrate the difference:
He left the house when the taxi arrived. (taxi arrived: punctual, point-in-time aspect)
He left the house while I was still sleeping. (I was still sleeping: durative, extended aspect)
There is sometimes a choice, to indicate the intended aspect:
He was in the playground when the children arrived. (They all came essentially at the same time.)
He was in the playground while the children arrived. (They came over a period of time.) (Here, children were arriving would probably be preferable.)