记四面体ＡＢＣＤ的四个面ＡＢＣ、ＡＣＤ、ＡＢＤ、ＢＣＤ分别为α、β、γ、δ;用αＡ、βＡ、γＡ 分别表示顶点Ａ的三个面角 ,其他顶点的三面角表示类似 ;用θＡＣ、θＢＤ等分别表示以ＡＣ、ＢＤ为棱的二面角的平面角。每个顶点的三个面角的和的一半记为该顶点字母 ,例如 The four faces ABC, ACD, ABD, and BCD of the tetrahedron ABCD are denoted as α, β, γ, and δ, respectively; the three face angles of the vertex A are represented by αA, βA, and γA, respectively, and the trihedral angles of the other vertices are similar; θAC, θBD, and the like respectively indicate plane angles of dihedral angles with AC and BD as ridges. A half of the sum of the three face angles of each vertex is recorded as the vertex letter, for example