Backslash in maps

[Suresh Govindachar]

Hello,

  Why does the following _single_ line map 
  generate the E10 error?:

  nmap <space> :let @a=substitute(getline('.'),'\(^.*|\s*\)\|\(\s\s*$\)','','g')

  How would it be fixed?

  Thanks,

  --Suresh