Overloading == error

g++ -c -o obj/main.o main.cpp -I../include
main.cpp:8:62: error: ‘bool coord::operator==(const coord&, const coord&)’ must take exactly one argument
     inline bool operator==(const coord& lhs, const coord& rhs){
                                                              ^
main.cpp: In function ‘int main()’:
main.cpp:24:6: error: no match for ‘operator==’ (operand types are ‘coord’ and ‘coord’)
  if(a==b){
      ^
main.cpp:24:6: note: candidates are:
In file included from /usr/include/c++/4.9.2/iosfwd:40:0,
                 from /usr/include/c++/4.9.2/ios:38,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/postypes.h:216:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
     ^
/usr/include/c++/4.9.2/bits/postypes.h:216:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::fpos<_StateT>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/4.9.2/bits/char_traits.h:39,
                 from /usr/include/c++/4.9.2/ios:40,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/stl_pair.h:214:5: note: template<class _T1, class _T2> bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
     ^
/usr/include/c++/4.9.2/bits/stl_pair.h:214:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::pair<_T1, _T2>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/4.9.2/bits/char_traits.h:39,
                 from /usr/include/c++/4.9.2/ios:40,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/stl_iterator.h:292:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
     operator==(const reverse_iterator<_Iterator>& __x,
     ^
/usr/include/c++/4.9.2/bits/stl_iterator.h:292:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::reverse_iterator<_Iterator>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/4.9.2/bits/char_traits.h:39,
                 from /usr/include/c++/4.9.2/ios:40,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/stl_iterator.h:342:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator==(const reverse_iterator<_IteratorL>& __x,
     ^
/usr/include/c++/4.9.2/bits/stl_iterator.h:342:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::reverse_iterator<_Iterator>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:41:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/allocator.h:128:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_T2>&)
     operator==(const allocator<_T1>&, const allocator<_T2>&)
     ^
/usr/include/c++/4.9.2/bits/allocator.h:128:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::allocator<_CharT>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:41:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/allocator.h:133:5: note: template<class _Tp> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_CharT>&)
     operator==(const allocator<_Tp>&, const allocator<_Tp>&)
     ^
/usr/include/c++/4.9.2/bits/allocator.h:133:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::allocator<_CharT>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:52:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/basic_string.h:2505:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^
/usr/include/c++/4.9.2/bits/basic_string.h:2505:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:52:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/basic_string.h:2512:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)
     operator==(const basic_string<_CharT>& __lhs,
     ^
/usr/include/c++/4.9.2/bits/basic_string.h:2512:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::basic_string<_CharT>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:52:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/basic_string.h:2526:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
     operator==(const _CharT* __lhs,
     ^
/usr/include/c++/4.9.2/bits/basic_string.h:2526:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   mismatched types ‘const _CharT*’ and ‘coord’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/string:52:0,
                 from /usr/include/c++/4.9.2/bits/locale_classes.h:40,
                 from /usr/include/c++/4.9.2/bits/ios_base.h:41,
                 from /usr/include/c++/4.9.2/ios:42,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/basic_string.h:2538:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^
/usr/include/c++/4.9.2/bits/basic_string.h:2538:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
  if(a==b){
        ^
In file included from /usr/include/c++/4.9.2/bits/locale_facets.h:48:0,
                 from /usr/include/c++/4.9.2/bits/basic_ios.h:37,
                 from /usr/include/c++/4.9.2/ios:44,
                 from /usr/include/c++/4.9.2/ostream:38,
                 from /usr/include/c++/4.9.2/iostream:39,
                 from main.cpp:1:
/usr/include/c++/4.9.2/bits/streambuf_iterator.h:204:5: note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&)
     operator==(const istreambuf_iterator<_CharT, _Traits>& __a,
     ^
/usr/include/c++/4.9.2/bits/streambuf_iterator.h:204:5: note:   template argument deduction/substitution failed:
main.cpp:24:8: note:   ‘coord’ is not derived from ‘const std::istreambuf_iterator<_CharT, _Traits>’
  if(a==b){
        ^
Makefile:17: recipe for target 'obj/main.o' failed
make: *** [obj/main.o] Error 1