Concept slug: radla_reisha_de_lo_ityada
First introduced: Op. 85
Last advanced: Op. 111
Appearance count: 7 chapters
radla (רישא דלא איתידע, Reisha delo ityeda, "the Unknown Head") is the highest concealed level — above Atik Yomin in the cosmogonic hierarchy. radla holds the root of the interconnections between MaH (gematria 45) and BaN (gematria 52) (Op. 85); the uncertainty it carries is structural, not merely epistemic. radla is unspecifiable in principle*.
radla is mentioned at Op. 64 (Reisha delo ityeda — first explicit appearance) but treated formally only in the Unknown Head unit (Op. 85–89). Op. 85 (the root of the interconnections between MaH and BaN lies in the Unknown Head while the results are found in the Partzufim, and both are concealed). Op. 86 (uncertainties — opposites that all exist). Op. 87 (the different combinations rule as one all the time and are unfathomable). Op. 88 (the Unknown Head contains all the interconnections; the uncertainty lies in trying to grasp it). Op. 89 (the Dew of Bedolach contrast — radla is unspecifiable, in distinction from the Dew which descends from A"A's head and in which all colours are seen).
The radla doctrine then operates as a discipline throughout the rest of the book: Op. 96 (the chain radla → Mitkala → AK → Atik → A"A → Atzilut — radla at the upstream end), Op. 100 (the underlying reasons are beyond comprehension — radla-respect operationalised). Op. 104 (the entire governmental order depends on the Three Heads and the Unknown Head). Op. 111 (radla referenced via the Beard's role for Zeir Anpin (Z"A)).
radla travels with Atik (the level immediately below — Atik receives the joining radla holds), MaH and BaN (whose interconnections are rooted in radla), concealed governmental order (radla is the deepest concealment), and Op. 1's Will/Essence restriction (radla extends the Op. 1 epistemic discipline upward into cosmogony).
radla is the cosmic-philosophical ceiling of investigation. Every later operational claim presupposes radla without claiming to penetrate it. The structural rule — the manner is investigable, the underlying reasons are not (Op. 100) — operates throughout the second half of Klach on the warrant of radla.