Hello again, I have found the appropriate section in the command reference under 'genr' The available Boolean operators are (again, in order of precedence): ! (negation), && (logical AND), || (logical OR), >, <, =, >= (greater than or equal), <= (less than or equal) and != (not equal). The Boolean operators can be used in constructing dummy variables: for instance (x > 10) returns 1 if x > 10, 0 otherwise. Sorry to bother you. Jan Von: Plus.line MailSystem [mailto:cyrus@mailer.plusline.de] Im Auftrag von Jan Tille Gesendet: Freitag, 9. September 2016 08:45 An: Gretl list <gretl-users(a)lists.wfu.edu&gt; Betreff: [Gretl-users] Boolean and / or in if-condtion (for example) Dear list members, I know my post is a consequence of my very modest programming skills, however, I think, others users might encounter this problem as well. I was trying to set up an if-command: if [condtion 1] = True and [condition 2] = True than do stuff endif In the first place, I used 'and' literally - I have to admit, that my first experience with if-conditions are from Excel-VBA. This of course produced an error-message. It took me while to figure out the solution. I remembered an R-tutorial which dealt with Boolean operators when I read the following post: http://lists.wfu.edu/pipermail/gretl-devel/2007-December/000714.html And most likely, my fault was to use the wrong operator 'and' instead of '&&'. Maybe I have missed it in the user guide, but it might be helpful, to put in a table that deals with logical operators &&, !, ||,etc. like true && true is true !true && false is true Maybe this is clear to anyone else, than you can of course disregard my post. Best regards Jan