# area #
MODE V = [2]REAL;
[] V vt = ((-1, -1), (1, -1), (1, 1.2), (-1, 1), (-2, 0.3));
PROC dp = (V a, V b)REAL:
  (REAL ss := 0; FOR j TO UPB a DO ss +:= a[j]*b[j] OD; ss);
PROC leng = (V v)REAL: sqrt(dp(v, v));
OP - = (V a, V b)V: (V c; FOR j TO UPB a DO c[j] := a[j] - b[j] OD; c);
OP * = (REAL b, V a)V: (V c; FOR j TO UPB a DO c[j] := a[j]*b OD; c);
(PROC ie = (INT i, j)REAL: (PROC ise = (INT i, j)REAL:
    (V tt = (vt[j] - vt[i]);
     V vn = (1.0/leng(tt))*tt;
     V vp = (vn[2], -vn[1]);
    dp(vt[i], vn)*dp(vt[i], vp));
  ise(i, j)-ise(j, i));
# Mysterious formula: #
(REAL tv := ie(UPB vt, 1); FOR j TO UPB vt - 1 DO tv +:= ie(j, j+1) OD;
print(tv/2.0)));
# Conventional formula: #
(PROC ae = (V a, b)REAL: (a[2]+b[2])*(a[1]-b[1])/2.0;
 REAL ss := ae(vt[UPB vt], vt[1]);
  FOR j TO UPB vt - 1 DO ss+:= ae(vt[j], vt[j+1]) OD; print (ss))