We are left with following problem, upon which TcT provides the
certificate YES(?,O(n^1)).

Strict Trs:
  { revapp(Cons(x, xs), rest) -> revapp(xs, Cons(x, rest))
  , revapp(Nil(), rest) -> rest
  , goal(xs, ys) -> revapp(xs, ys) }
Obligation:
  innermost runtime complexity
Answer:
  YES(?,O(n^1))

The input was oriented with the instance of 'Small Polynomial Path
Order (PS,1-bounded)' as induced by the safe mapping

 safe(revapp) = {2}, safe(Cons) = {1, 2}, safe(Nil) = {},
 safe(goal) = {}

and precedence

 goal > revapp .

Following symbols are considered recursive:

 {revapp}

The recursion depth is 1.

For your convenience, here are the satisfied ordering constraints:

  revapp(Cons(; x,  xs); rest) > revapp(xs; Cons(; x,  rest))
                                                             
           revapp(Nil(); rest) > rest                        
                                                             
                goal(xs,  ys;) > revapp(xs; ys)              
                                                             

Hurray, we answered YES(?,O(n^1))