View Compilation Error

0_0_21559410_19861.cpp: In function 'void tb()':
0_0_21559410_19861.cpp:61:60: error: no matching function for call to 'P::det(P)'
   while (k > 1 && (p[k - 1] - p[k - 2]).det(a[i] - p[k - 1]) < 0)
                                                            ^
0_0_21559410_19861.cpp:61:60: note: candidate is:
0_0_21559410_19861.cpp:41:6: note: int P::det(P&)
  int det(P &a)
      ^
0_0_21559410_19861.cpp:41:6: note:   no known conversion for argument 1 from 'P' to 'P&'
0_0_21559410_19861.cpp:67:60: error: no matching function for call to 'P::det(P)'
   while (k > t && (p[k - 1] - p[k - 2]).det(a[i] - p[k - 1]) < 0)
                                                            ^
0_0_21559410_19861.cpp:67:60: note: candidate is:
0_0_21559410_19861.cpp:41:6: note: int P::det(P&)
  int det(P &a)
      ^
0_0_21559410_19861.cpp:41:6: note:   no known conversion for argument 1 from 'P' to 'P&'