Let G be a graph with vertex set V and edge set E , and let A be an abelian group. A labeling f : V → A induces an edge labeling f ∗ : E → A defined by f (xy) = f (x) + f (y). For i ∈ A, let v f (i) = card{v ∈ V : f (v) = i} and e f (i) = card{e ∈ E : f (e) = i}. A labeling f is said to be A-friendly if |v f (i)−v f ( j)| ≤ 1 for all (i, j) ∈ A× A, and A-cordial if we also have |e f (i) − e f (...