const m3 = {
  xRotation: (phi) => {
    const c = Math.cos(phi), s = Math.sin(phi);
    return [
      1,  0,  0,
      0,  c, -s,
      0,  s,  c
    ];
  },
  yRotation: (phi) => {
    const c = Math.cos(phi), s = Math.sin(phi);
    return [
       c, 0, s,
       0, 1, 0,
       -s, 0, c
    ];
  },
  zRotation: (phi) => {
    const c = Math.cos(phi), s = Math.sin(phi);
    return [
      c, -s, 0,
      s,  c, 0,
      0,  0, 1
    ];
  },
  add: (m1, m2) => [
    m1[0] + m2[0],
    m1[1] + m2[1],
    m1[2] + m2[2],
    m1[3] + m2[3],
    m1[4] + m2[4],
    m1[5] + m2[5],
    m1[6] + m2[6],
    m1[7] + m2[7],
    m1[8] + m2[8],
  ],
  mul: (m1, m2) => [
    m1[0]*m2[0] + m1[1]*m2[3] + m1[2]*m2[6],
    m1[0]*m2[1] + m1[1]*m2[4] + m1[2]*m2[7],
    m1[0]*m2[2] + m1[1]*m2[5] + m1[2]*m2[8],
    m1[3]*m2[0] + m1[4]*m2[3] + m1[5]*m2[6],
    m1[3]*m2[1] + m1[4]*m2[4] + m1[5]*m2[7],
    m1[3]*m2[2] + m1[4]*m2[5] + m1[5]*m2[8],
    m1[6]*m2[0] + m1[7]*m2[3] + m1[8]*m2[6],
    m1[6]*m2[1] + m1[7]*m2[4] + m1[8]*m2[7],
    m1[6]*m2[2] + m1[7]*m2[5] + m1[8]*m2[8],
  ],
  mulV: (m, v) => [
    m[0]*v[0] + m[1]*v[1] + m[2]*v[2],
    m[3]*v[0] + m[4]*v[1] + m[5]*v[2],
    m[6]*v[0] + m[7]*v[1] + m[8]*v[2]
  ],
  eq: (m1, m2) =>
    m1[0] === m2[0] &&
    m1[1] === m2[1] &&
    m1[2] === m2[2] &&
    m1[3] === m2[3] &&
    m1[4] === m2[4] &&
    m1[5] === m2[5] &&
    m1[6] === m2[6] &&
    m1[7] === m2[7] &&
    m1[8] === m2[8],
};