Issue with include

I use many includes within my views also depending on passed parameters different HTML headers are loaded (a special one for AmpProject compatible pages.)

Recently CodeIgniter simplified includes by declaring a VIEWPATH constant in index.php.

// view file common to many web-pages
if( isset( $ampOk ) ):
require VIEWPATH ."template/core/_header-amp.php";
else:
// load non-amp version
endif;


Tediously tapped on a tablet