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,B,A
let A, B, C be POINT of S; :: thesis: ( not {A,B,C} is linear implies Plane A,B,C = Plane C,B,A )
assume A1: not {A,B,C} is linear ; :: thesis: Plane A,B,C = Plane C,B,A
then A2: not {C,B,A} is linear by ENUMSET1:102;
thus Plane A,B,C = Plane C,A,B by A1, Th61
.= Plane C,B,A by A2, Th58 ; :: thesis: verum