Goal:
    z : t  hd : A.t  tl : list A.t  H1' : list A.t  H1 : t  H : lt_ H1' H1
  ============================
   ({| pr1 := hd :: tl; pr2 := z |} = {| pr1 := H1'; pr2 := H1 |} ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in lt [] z)


DEBUG:Going to execute:
DepElim.decompose_exists id id'