(roughly translated from German)The difference between <header_name> and "header_name" lies in the strategy used to find the include file.<header_name>This form specifies a default include file. The compiler will search for it successively in all default directories (in the order of their definitions). An error is raised if it can't be found."header_name"This form specifies a user defined include file. It may be used with a absolute or relative path. If it can't be found, then the compiler will search for it the same way like if <header_name> is used.