MAYBE

'Pop* with parameter subtitution (timeout of 60.0 seconds)'
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Answer:           MAYBE
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  sum(cons(s(n), x), cons(m, y)) -> sum(cons(n, x), cons(s(m), y))
     , sum(cons(0(), x), y) -> sum(x, y)
     , sum(nil(), y) -> y
     , empty(nil()) -> true()
     , empty(cons(n, x)) -> false()
     , tail(nil()) -> nil()
     , tail(cons(n, x)) -> x
     , head(cons(n, x)) -> n
     , weight(x) -> if(empty(x), empty(tail(x)), x)
     , if(true(), b, x) -> weight_undefined_error()
     , if(false(), b, x) -> if2(b, x)
     , if2(true(), x) -> head(x)
     , if2(false(), x) -> weight(sum(x, cons(0(), tail(tail(x)))))}

Proof Output:    
  The input cannot be shown compatible