let n be Nat; ( not n <= 11 or n = 0 or n = 1 or n = 2 or n = 3 or n = 4 or n = 5 or n = 6 or n = 7 or n = 8 or n = 9 or n = 10 or n = 11 )
assume
n <= 11
; ( n = 0 or n = 1 or n = 2 or n = 3 or n = 4 or n = 5 or n = 6 or n = 7 or n = 8 or n = 9 or n = 10 or n = 11 )
then
n <= 10 + 1
;
hence
( n = 0 or n = 1 or n = 2 or n = 3 or n = 4 or n = 5 or n = 6 or n = 7 or n = 8 or n = 9 or n = 10 or n = 11 )
by Th8, Th35; verum