Dear Tristan, you can do it as follows:
p1 = 5; % initialize p1
a = p1; % store p1 value in new variable to use later
p2 = 3; % initialize p2
p1 = p1 - p2; % overwrite value of p1
p2 = a + p2; % use old value of p1 to overwrite p2
I hope it helps. Good luck!
