I am looking for ideas how to make TeX understand that when # appears both in the if-else and in the else-fi part of a conditional in an alignment tab, in the end there will never be more than one # in the tab. Here is some sample code:
\def\table{
\halign{
\iftrue\hfil##\else##\hfil\fi\cr
Bla-bla\cr}}
\table