# Paul Wiereyn

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Paul H. Wiereyn,
a Dutch chess problem composer and chess solving engine and GUI programmer. He is author of a free Sudoku program and the Windows GUI APwin for the chess problem solving programs Alybadix and Popeye.

# 0x88

In his 1985 paper Inventive Problem Solving [1], Paul Wiereyn described 0x88 coordinates with nibbles for ranks and files inside a byte, and used such square differences (mod 256) as table-index to determine pinned pieces and discovered checks in his problem solving program:

```It is obvious to chess-players that a piece when pinned should not be allowed to move out of the direction in which it is pinned. Hence, as a preliminary, we calculate, in one byte, the difference between the coordinates of the piece about to be moved and one's own King, e.g.,
```
```Rd5 - Kf5 <=> 45 - 65 = E0, hexadecimals and reduction modulo 256
```
```being implied throughout.
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```The difference, E0 say, serves to enter a table T. The tabular value T[E0] so found, when zero, indicates non-collinearity (the pieces are not on the same rank, file or (co-)diagonal). If not zero, the value codes the direction of collinearity, i.e., the pinning direction. In our example the value T[E0] = F0, stands for due West.
```