split <;> simp
tag : Tag
time : Time.From tag.time
⊢ (if tag.time < time.val then { time := time.val, microstep := 0 } else increment tag).time = time.val
case inr
tag : Tag
time : Time.From tag.time
h✝ : ¬tag.time < time.val
⊢ (increment tag).time = time.val