Puzzle #598 - Packing (Pentominous)

Some time ago there was some discussion on pentomino packing in an 8x8 square with 4 cells removed, and what layouts were impossible to fit 1 copy of each into. After the obvious cases of sectioning off part of the grid, someone mentioned forcing two P pentominoes. I quickly made an empty grid to mock it up, and then realized it would actually make a good Pentominous opening. So I made that, too.

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