STL set/map w.r.t const char*

Hi

I have a very basic question, but it's a good one. Below is the code
fragment.

struct ltstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return strcmp(s1, s2) < 0;
  }
};

int main()
{
  const int N = 6;
  const char* a[N] = {"isomer", "ephemeral", "prosaic",
                      "nugatory", "artichoke", "serif"};
  set<const char*, ltstr> A(a, a + N);
  if (A.find("ephemeral") != A.end())
    cout << "Found";
  else
    cout << "Not found";
  return 0;
}

Output will be -> "Found"
My question is , Why?

How it is able to compare a const char* with another const char* to
find that value? I did not specify any equality operator? I just
mentioned strcmp(s1, s2) < 0
which means, when strcmp(s1, s2) == 0 (in case of match)
it will return false. So how set/map are able to find the const char*
value?