185c185
< pf.erase(iter);
---
> iter = pf.erase(iter);
197c197,198
< iter--;
---
> if (iter != pf.begin())
> iter--;
204,205c205,207
< pf.erase(iter);
< iter--;
---
> iter = pf.erase(iter);
> if (iter != pf.begin())
> iter--;