Documentation for processing - substitution

[k4rst3ns]

• missing general comment in realization.gms (A bit more detail on the purpose of this realization would be helpful. Maybe add Limitations also. I think it's better to have the realization descriptions independent of other realizations, so that they are still clear if the other (referred to) realization is deleted one day.)

• equation comments:

  • L9: is "aggregation" the right word here? I don't understand the sentence entirely...
  • L12: Why do we want to replicate the structure? The end result is what matters, no?
  • utility?

• presolve

  • I always thought that when we set .fx we don't (shouldn't) set .up and .lo
  • using i or i2 in presolve? (it is mixed here)