Symplectic Geometry
《Symplectic Geometry》 · 第 19–20 页 · Section 1.8，Figure 1.14 中间左图及 The Whitehead link 段落（完整链环图）
The Whitehead link. The diagram in the centre-left of Figure 1.14 shows a 2-component link with orientations marked, and the components labelled 1 and 2. This is the labelled oriented link \(5^2_1++\). (The unlabelled unoriented link is denoted simply by \(5^2_1\).)