[latex]ain{1,2,3,4,5,6} \ \ 2ain{2,4,6,8,10,12} \ \ 2a-1in{1,3,5,7,9,11} \ \ xin{1,3,5,7,9,11}[/latex]

x =2a -1 a ∈ { 1 ;2 ;3 ; 4 ; 5 ;6 } *2 2a ∈ {2 ;4 ;6 ;8 ;10 ;12 } 2a-1 ∈{1 ;3 ;5 ;7 ; 9 ;11 } x ∈ {1 ;3 ;5 ; 7 ;9 ;11 }