Polyominous

Rules

Divide the grid into set of given polyominoes such that every cell in the grid is part of exactly one polyomino. Polyminoes of the same shape (rotations and reflections of a polyomino count as the same shape) cannot touch each other along an edge (but they may touch diagonally). Some letters are given in the grid. Each letter must be part of a polyomino with that letter’s shape. It is permissible for a polyomino to contain more than one letter. (It is possible for some polyomino shapes to never appear in the grid, or more than once.) The letter-to-shape correspondence for polyominoes has been supplied for you.

(Rules (modified) and example (using Pentominoes) from PGP IB)

Rule variations

• Most of the puzzles appears as either Pentominous (using 12 pentominoes) or Tetrominous/LITSO (5 tetrominoes).
• Borders can be given as hints.
• Pentominous Nontouching: Appeared on WPC 2019/Round 10. Congruent regions don't touch each other even diagonally.

History of the puzzle

The version that uses pentominoes first appeared on GM Puzzles in 2013. Invented by Grant Fikes (USA) as a variant of Fillomino. Polyominous was originally the name Fikes gave to Fillomino in his blog.

However, the version that uses 5 tetrominoes predates this. For example, Forsmarts 7th Anniversary Contest (2011) had one under the name Untouchable Tetra. Puzzle BOOKS 1 (2008) published by Sekaibunkasha and written by Shin'ichi Aoki (Japan) in 2008 had some under the name LITSO. Most likely LITSO came earlier in the Puzzler magazine.

Variants

Second Seen

Probably first appeared on WPC 2018/Round 8, written by by Petr Vejchoda (Czech Rep.). Hybrid with Easy as clues. Somehow it was named "Tetrominoes End View" though the clues were referencing second tetromino.

Additional rules: Some letters are given outside the grid. Each of those letters represents the second tetromino that can be seen in the respective row or column from the respective direction.

(Rules and example from PGP IB)

Appearances in the past WPCs

• WPC 2019/Round 3 (Permaculture hybrid with Arukone) by Silke Berendes
• WPC 2019/Round 10 (Nontouching) by Sebastian Matschke
• WPC 2018/Round 8 by Jan Zvěřina
• WPC 2018/Round 8 (Second Seen) by Petr Vejchoda