Questions for sentences in Phaedrus's «Aesopus Latinus»

Question

I have some problems in understanding these sentences in Phaedrus, III.7 (the wolf and the dog):

• Canis simpliciter: "Eadem est condiciō tibi, praestāre dominō sī pār officium potes."

Why is an infinitive praestāre here? Is it for potes? If so what is the verb for the sī clause? or is the infinitive hortative/imperative?

• "Quod?" inquit ille (:=lupus). [Canis:] "Cūstōs ut sīs līminis..."

Is the ut optative?

• crepusculō solūtus quā vīsum est vagor.

= "At dusk when I am allowed, I wander, being solved." ?

• [Lupus:] "Fruere quae laudās, canis! Rēgnāre nōlō, līber ut nōn sim mihī."

Why does it say "I don't want to rule, so that I may not be free"? What's the logic here?

Answer 1

• Canis simpliciter: "Eadem est condiciō tibi, praestāre dominō sī pār officium potes."

  = sī potes [quid?] pār officium [cui?] dominō [quid facere?] praestāre

• "Quod?" inquit ille (:=lupus). [Canis:] "Cūstōs ut sīs līminis..."

  = quod officium? ut custōs sīs līminis. It's a description of the duty, 'to guard the entrance'.

  crepusculō solūtus quā vīsum est vagor.

  solūtus = catēnīs solūtus, expedītus, līber; quā vīsum est = quālibet, quācumque volō

• Rēgnāre nōlō, līber ut nōn sim mihī."

  = nōlō ita rēgnāre ut līber mihimet nōn sim. quī līber nōn est sibi, nōn rēgnat sed servit