anchor.diff:  
   -type do_get_header_by_hash_reply() ::
           {ok, header()} |
  -        {error, Reason::{header_not_found, Details::{top_header, header()}}}.
  +        {error, Reason::{header_not_found, {top_header, header()}}}.
   -spec do_get_header_by_hash(block_header_hash(), header(), headers_db()) ->
                                      do_get_header_by_hash_reply().
   do_get_header_by_hash(HeaderHash, TopHeader, HeadersDb) ->
  
positive.code: 
  -type do_get_block_by_height_reply() ::
          {ok, block()} |
          {error, Reason::{chain_too_short, Details::{{chain_height, height()},
                                                      {top_header, header()}}} |
                          {block_not_found, {top_header, header()}}
          }.
  -spec do_get_block_by_height(height(), header(), headers_db(), blocks_db()) ->
  
negative.code: 
  -type do_get_header_by_height_reply() ::
          {ok, header()} |
          {error, Reason::{chain_too_short, {{chain_height, height()},
                                             {top_header, header()}}}}.
  -spec do_get_header_by_height(height(), header(), headers_db()) ->
                                       do_get_header_by_height_reply().
  do_get_header_by_height(Height, TopHeader, HeadersDb) ->
  