let S be IncSpace; :: thesis: for A, B, C being POINT of S st not {A,B,C} is linear holds
Plane A,B,C = Plane C,A,B
let A, B, C be POINT of S; :: thesis: ( not {A,B,C} is linear implies Plane A,B,C = Plane C,A,B )
assume A1: not {A,B,C} is linear ; :: thesis: Plane A,B,C = Plane C,A,B
then A2: not {C,A,B} is linear by ENUMSET1:100;
thus Plane A,B,C = Plane A,C,B by A1, Th58
.= Plane C,A,B by A2, Th59 ; :: thesis: verum