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simple way how each plane intersecting aj, ag, az, a4 also cuts as. 
If we introduce for the determinant pz qi — gi pr the notation (Xl) 
the four conditions can be written in the form 
(58) + (61) + (18) = 0 
(54) + (52) + (24) = 0 
(25) + (85) + (23) =0 | 
(15) + (45) + (14) = 0 
So addition gives 
(13) + (14) + (23) + (24) = 0, 
which is the condition that the plane cuts the line a;. For 
substituting 
y= V9 5 Ve == v4, 3 v5 = 0 
into pe = 0 and gz =O we find 
(py + pg) t2 + (ps + pa) % = 9, 
(9, + 92) 22 + (9s: + Ga) 4 — Ue 
Bia Fe : XH 
by eliminating the quotient — we get 
Ty, 
Pipe 1 Pst Pa 
—_— : 
M+% + I + 4 
which can be immediately developed into 
(18) + (14) + (23) + @4) = 0. 
6. Now that we have found the equation of the enveloped 
space the full investigation of it may be omitted. We shall confine 
ourselves to some ready observations. 
