let $g=(v,e)$ be a simple graph. an edge labeling $f:eto {0,1}$ induces a vertex labeling $f^+:vtoz_2$ defined by $f^+(v)equiv sumlimits_{uvin e} f(uv)pmod{2}$ for each $v in v$, where $z_2={0,1}$ is the additive group of order 2. for $iin{0,1}$, let $e_f(i)=|f^{-1}(i)|$ and $v_f(i)=|(f^+)^{-1}(i)|$. a labeling $f$ is called edge-friendly if $|e_f(1)-e_f(0)|le 1$. $i_f(g)=v_f(...