Easiest way is a vise. Hold the post, pull the frame while working side to side. Second easiest way, step into the V where the down and seat tubes meet, with yiur hip stabilizing the frame from twisting. Use one tool to turn the post, and the other hand to grip and pull on the post as you turn. This method works twist in one direction continuously.
Either way usually causes some heat so keep the post well oiled with penetrant, and rest it to cool as needed.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.