ltbw tlbw lbtw bltw tblw btlw ltwb tlwb lwtb wltb twlb wtlb lbwt blwt lwbt wlbt bwlt wblt tbwl btwl twbl wtbl bwtl wbtl
Note: these 'words' (valid or invalid) are all the permutations of the word ltbw. These words are obtained by scrambling the letters in ltbw.