---- h1
10
---- h2
3
10
0
---- h3
10
30
4
---- inv
10
match1.lean:82:0: error: type mismatch during dependent match-elimination at pattern variable 'w' with type
  VecPred P Vec.nil
expected type
  VecPred P tail✝
[false, true, true]
match1.lean:113:0: error: dependent match elimination failed, inaccessible pattern found 
  .(j + j)
constructor expected
[false, true, true]