firns ifrns frins rfins irfns rifns finrs ifnrs fnirs nfirs infrs nifrs frnis rfnis fnris nfris rnfis nrfis irnfs rinfs inrfs nirfs rnifs nrifs firsn ifrsn frisn rfisn irfsn rifsn fisrn ifsrn fsirn sfirn isfrn sifrn frsin rfsin fsrin sfrin rsfin srfin irsfn risfn isrfn sirfn rsifn srifn finsr ifnsr fnisr nfisr infsr nifsr fisnr ifsnr fsinr sfinr isfnr sifnr fnsir nfsir fsnir sfnir nsfir snfir insfr nisfr isnfr sinfr nsifr snifr frnsi rfnsi fnrsi nfrsi rnfsi nrfsi frsni rfsni fsrni sfrni rsfni srfni fnsri nfsri fsnri sfnri nsfri snfri rnsfi nrsfi rsnfi srnfi nsrfi snrfi irnsf rinsf inrsf nirsf rnisf nrisf irsnf risnf isrnf sirnf rsinf srinf insrf nisrf isnrf sinrf nsirf snirf rnsif nrsif rsnif srnif nsrif snrif
Note: these 'words' (valid or invalid) are all the permutations of the word firns. These words are obtained by scrambling the letters in firns.