let S be IncSpace; :: thesis: for A being POINT of S holds
not for B, C, D being POINT of S holds {A,B,C,D} is planar
let A be POINT of S; :: thesis: not for B, C, D being POINT of S holds {A,B,C,D} is planar
consider L being LINE of S;
consider B being POINT of S such that
A1: A <> B and
B on L by Lm1;
not for C, D being POINT of S holds {A,B,C,D} is planar by A1, Th77;
hence not for B, C, D being POINT of S holds {A,B,C,D} is planar ; :: thesis: verum