Katakana spelling is common for this go term; usually written in kana.
Kanji spelling using 堅 (firm/solid); rarely used in practice.
Mixed kana-kanji spelling given; less common than the pure katakana form.
Kanji spelling using 固 (hard/solid); rarely used in practice.
Compound of カタ (kata, 'solid, hard') and ツギ (tsugi, 'connection'), a go term. The exact historical derivation is uncertain, but it follows the pattern of go terminology combining descriptive prefixes with ツギ.