AC_CHECK_HEADER(S) search path

[Genty Jean-Paul]

  Hi

  Wich directory variable should I set to tell AC_CHECK_HEADER to search in  ??

  For instance I have installed a package in /usr/local/mylib/include and 
/usr/local/mylib/lib and I would like configure to detect if mylib is not 
installed.
  I prefer not to put it in an environnement variable.

  Thanks

Jean-Paul