Theorem - The contact number is sorted vertically only be a natural straight line that gives a natural gap
-When has two (more) solutions they are connected
Proof -[tex]1\rightarrow \underline1(\underline{s})[/tex]
[tex]4{+_{12}^{0}}2=\underline2[/tex] or [tex]4{+_{12}^{\underline4}}2= \underline2[/tex]
[tex]4{+_{12}^{1}}2=\underline2[/tex] or [tex]4{+_{12}^{\underline3}}2= \underline2[/tex]
[tex]4{+_{12}^{2}}2=\underline2[/tex] or [tex]4{+_{12}^{\underline2}}2= \underline2[/tex]
[tex]4{+_{12}^{3}}2=\underline4[/tex] or [tex]4{+_{12}^{\underline1}}2= \underline4[/tex]
[tex]4{+_{12}^{4}}2=\underline6[/tex] or [tex]4{+_{12}^{\underline0}}2= \underline6[/tex]
[tex]+_{12}[/tex]- addition rule 12
(CM.) - no addition rule 12