Sun and Shade
This puzzle appears to have been developed by Erich Friedman.
Puzzle and Goal
An unsolved puzzle consists of a square grid. Some of the cells contain number clues.
The goal is to color in some of the cells according to the rules.
The solved grid must satisfy the following conditions:
Clues indicate the total number of neighboring cells (including diagonally) that are colored.
If a cell is colored, then a total of exactly two other cells in the same ranks (rows and columns) must also be colored (that is, either two in the same row, two in the same column, or one in the same row and one in the same column).