G
D
σ(G) D · GROUP ACTION ℤ/2ℤ · INNER CURVES FACE · FIELD ENCLOSED · ◈
DEFINITION
Let G ∈ ℝ² be the letterform. Let σ: x ↦ (2a−x, y) be reflection across x=a.
σ(G) = G reflected. The pair {σ(G), D} placed at x=a creates bilateral symmetry.
The region between inner curves: a simply-connected domain Ω ⊂ ℝ². ∂Ω = the seal. ∎