typedef struct Vector {
  double x1;
  double x2;
} Vector;

typedef struct Matrix {
  double a11;
  double a12;
  double a21;
  double a22;
} Matrix;

struct Matrix multiply(struct Matrix m1, struct Matrix m2) {
  Matrix r = {
      .a11 = m1.a11*m2.a11 + m1.a12*m2.a21,
      .a12 = m1.a11*m2.a12 + m1.a12*m2.a22,
      .a21 = m1.a21*m2.a11 + m1.a22*m2.a21,
      .a22 = m1.a21*m2.a12 + m1.a22*m2.a22
    };
  return r;
};

struct Vector multiply(struct Matrix m, struct Vector v) {
  Vector r = {
      .x1 = (m.a11*v.x1) + (m.a12*v.x2),
      .x2 = (m.a21*v.x1) + (m.a22*v.x2)
    };
  return r;
}

struct Vector add(struct Vector v1, struct Vector v2) {
  Vector r = {
    .x1 = v1.x1 + v2.x2,
    .x2 = v1.x2 + v2.x2
  };
  return r;
}