From: ciapecki [mailto:ciapecki / gmail.com] 
> > irb(main):006:0> s.gsub( /\b([a-z]) (?=[a-z]\b)/i, '\\1' )
> > => "A long cat and a quick mouse met oj simpson on the tcp stack"
> 
> this is exactly what I need.
> Is it possible to rewrite it without using lookahead (?=subexp)  ?

I don't think so, unless you have a positive lookbehind instead.

Why don't you want the lookahead? Are you actually using this regexp
with a language other than Ruby?