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A(1;0;-1)B(2;2;3)C(3;1;-2)D(-4;2;1)
ABC
(ABC)
(ABC)
ABC
ABC
D(ABC)DABC
(S)
(ABC)
(ABC)
(ABC)(S)
(P)(P)(ABC)
(P)(ABC)
D(P)D
t’
D
(Q)[MN]
(P)(Q)(ABC)
GG'GABCG'
M