In the described case ‘N50’ can be left out. Maybe this coe is clearer to understand:<pre>if *in50;
Logically, there is no point to having N50 on the line. The line should never be reached unless 50 is off, so there is no logical reason for having the N50. (“N50” means indicator 50 is “not” on.)
It is possible that the N50 line was in the program from the beginning, and the 50 line was added later. When the 50 line was added, the programmer could have removed “N50” but forgot to do so or chose not to make changes that weren’t absolutely required.
Or the programmer was simply unsure how indicators worked.
Regardless, when the 50 line LEAVEs the block of code, the N50 condition doesn’t have to be specified.