LITS: blocks and connections
No 2×2 block may be all shaded, and the shading must be one piece. Both rules rule out fits, and when they run out, try a cell and see what breaks.
How it works
No 2×2: a fit that finishes a 2×2 block with shading already there is out. In short, when three cells of a square are shaded, the fourth is not.
Stay connected: all the shading is one piece. A fit that would leave some shading, or some region, cut off from the rest is out.
When neither moves, try it and see: suppose a cell is unshaded and follow the rules. If some region is left with no fit, the cell is shaded.
Why connection is strong
Every region has a tetromino, and every tetromino must join the rest. So a region in a corner must reach out toward its neighbours, and a region between two others often has to bridge them.
Look at where two finished tetrominoes would have to meet. The cells between them are often the only bridge.
Worth memorizing
Three shaded in a square: the fourth is not.
One connected shape.
A fit that strands shading is out.
Stuck? Suppose a cell is unshaded.
If a region runs out of fits, it is shaded.
Practice
0 of 4 rightWhat is the ringed cell?
Using region overlap only, what is the ringed cell?
What is the ringed cell?
Try it and see: what is the ringed cell?