anchor.diff:  centre(String, 0, Char) when is_list(String), is_integer(Char) ->
       [];                       % Strange cases to centre string
   centre(String, Len, Char) when is_integer(Char) ->
  -    Slen = length(String),
  +    Slen = erlang:length(String),
       if
   	Slen > Len -> substr(String, (Slen-Len) div 2 + 1, Len);
   	Slen < Len ->
  
positive.code:       String :: string(),
        Length :: non_neg_integer().
  
  len(S) -> length(S).
  
  %% equal(String1, String2)
  %%  Test if 2 strings are equal.
  
negative.code:     end.
  
  to_number(String, Number, Rest, List, _Tail) when is_binary(String) ->
      BSz = erlang:length(List)-erlang:length(Rest),
      <<_:BSz/binary, Cont/binary>> = String,
      {Number, Cont};
  to_number(_, Number, Rest, _, Tail) ->
  