reconsider a = 1, b = 2, c = 3 as Point of CLS by ENUMSET1:def 1;
take
a
; not for b, c being Point of CLS holds a,b,c are_collinear
take
b
; not for c being Point of CLS holds a,b,c are_collinear
take
c
; not a,b,c are_collinear
not [a,b,c] in the Collinearity of CLS
by Lm5;
hence
not a,b,c are_collinear
; verum