I had an 'l' for '1' error half a century ago in FORTRAN code, keyed in by me on punch cards. The line printer printout of my code distinguished the two symbol

I had an 'l' for '1' error half a century ago in FORTRAN code, keyed in by me on punch cards. The line printer printout of my code distinguished the two symbols, but the ribbon was old and the distinction was nearly--not entirely--obliterated in print.