test1.pl:2     use strict;
test1.pl:4     use lib qq{/usr/web/wonko/test/lib/SYS};
test1.pl:5     use lib qq{/usr/web/wonko/test/lib/AB};
test1.pl:7     require SYS_mail;

   Start executing SYS_mail.pm

SYS_mail.pm:1  package SYS_mail;
SYS_mail.pm:3  use lib qq{/usr/web/wonko/test/lib/AB};
SYS_mail.pm:5  require AB_prod;

   Start executing AB_prod.pm

AB_prod.pm:1   package AB_prod;
AB_prod.pm:3   use lib qq{/usr/web/wonko/test/lib/SYS};
AB_prod.pm:5   require SYS_mail;

   Does nothing. Already required

AB_prod.pm:5   SYS_mail->import(qw ( send_mail ))
                  if SYS_mail->can('import');

   ERROR!!