Because of the unsless of the redundant words and the double words
which have no semantic meaning in the process of combination (such as: "de ren" and "le mei"), so we filter the redundant elements and none semantic words by calculating the correlation of elements T, word1 and word2 in the collection to assure the constitute way of the single words in the text.
The number of 6x6 double word
squares constructible with TWL06 is about 1/200th the number of 5x5 squares, and the odds of a tour accidentally spelling six 6-letter words is significantly smaller than the odds of spelling five 5-letter words.
squares are, of course, more difficult, but there are 20 different possibilities, from OBAMA and BIDEN in lines 1 and 2 to BIDEN and OBAMA in lines 4 and 5.
This is intermediate in difficulty between an 8-by-8 and a 9-by-9 double word
square, the latter of which has never been done in English.
A quick addendum to McManus's "Sudoku Patterns"--One can insert in the three diagonal 3x3 regions three double word
squares with no words in common: SPA/ORT/DYE, SPY/ARE/DOT and ROD/APE/STY.
All words in the double eight-square can be found in dictionaries, with thirteen of them in the OED or Web 2 ["Double Word
Squares," WW, Feb 1972].