Consider two processes P₁ and P₂ accessing the shared variables X and Y…

Consider two processes P₁ and P₂ accessing the shared variables X and Y protected by two binary semaphores Sₓ and Sᵧ respectively, both initialized to 1. P and V denote the usual semaphore operators, where P decrements the semaphore value, and V increments the semaphore value. The pseudo-code of P₁ and P₂ is as follows:

P₁:
while true do {
  L₁: ......
  L₂: ......
  X = X + 1;
  Y = Y - 1;
  V(Sₓ);
  V(Sᵧ);
}

P₂:
while true do {
  L₃: ......
  L₄: ......
  Y = Y + 1;
  X = X - 1;
  V(Sᵧ);
  V(Sₓ);
}

In order to avoid deadlock, the correct operators at L₁, L₂, L₃ and L₄ are respectively.