On Mar 16, 7:38 pm, WM <mueck...@rz.fh-augsburg.de> wrote: > On 16 Mrz., 19:26, William Hughes <wpihug...@gmail.com> wrote: > > > > > > > > > > > On Mar 16, 7:10 pm, WM <mueck...@rz.fh-augsburg.de> wrote: > > > > On 16 Mrz., 18:10, William Hughes <wpihug...@gmail.com> wrote: > > > > > > Ok, I understand. Anyhow, if the number of lines is not empty, then > > > > > there must remain at least one line as a necessary line. > > > > > Not a particular line. This is similar to > > > > the case where any set of lines with an unfindable > > > > last line has at least one "necessary" findable line. > > > > This line has a line number in the original > > > > list but we can choose the "necessary" > > > > findable line to have any line number we want. > > > > No, it is always the last line. We call it unfindable or unfixable > > > because as soon as we have found it, it is no longer the last line. > > > Note, that I am not talking about the unfindable line, > > but the "necessary" findable line. We can choose this > > line to have any line number we want > > In potential infinity there is no necessary line except the last one. > We know that with certainty from induction. Every found and fixed line > n cannot be necessary, because the next line contains it.
And yet you agree that for a set of lines to contain an unfindable line it is necessary that it contain at least two findable lines.