I have just released a new puzzle book:

For the time being, you can only buy it
from Lulu
in print for AU$ 9.99 or from Smashwords
in various e-book formats for US$ 1.99. It will take a while before
you will find it on Amazon, Barnes & Noble, etc. It always does.

This book contains 100 difficult
CalcuDoku puzzles. CalcuDokus, introduced in 004 as KenKen® (a
registered trademark of Nextoy LLC), is a 9x9 numeric puzzle similar
to Sudoku. But, unlike Sudoku, CalcuDoku doesn’t require you to
learn complex strategies.

Each cage contains a target number and
a code to indicate one of the four basic operations: “x”, “+”,
“-”, and “:”. To solve a CalcuDoku puzzle, you have to solve
all its cages; and to solve each cage you must write in its cells the
digits that give you the cage target when you apply to them the cage
operation.

Unless a cage consists of a single cell
(in which case there is no operation and its solution coincides with
its target), you can solve it in several ways. For example, a 2-cell
cage marked “7+” admits six solutions: 61, 16, 52, 25, 43, and
34. But only one of those solutions is correct and will let you solve
the whole puzzle.

You can discard the wrong solutions of
all cages by repeatedly applying the rule that each digit between 1
and 9 can only appear once in each row and column.

The first sixty puzzles of this book
consist of randomly generated cages, like the following one:

They are difficult, but I limited their
difficulty by setting to 2 the maximum number of cages admitting more
than 200 combinations. Therefore, although I haven’t tried them
all, I’m pretty confident that they can be solved analytically.
That is, without having to guess.

To create the other forty puzzles, I
used a different strategy: instead of generating random cages, I
arranged them in fixed patterns and only generated random digits,
targets, and op-codes. Here is the type of puzzle you can expect:

These puzzles are in most (but not all)
cases more difficult than the random ones. In fact some of them are
quite diabolical. The first couple of patterned puzzles are easier
than those that follow. Otherwise, the difficulty of the puzzles
varies in no particular order.

Of the pattern-puzzles, I solved those
numbered from 61 to 98. I haven't solved puzzle 99 but I believe it
should be possible to complete it without having to guess (which I
never do). Puzzle 100 is a different type of challenge: it admits two
solutions, which differ in three cages. I could have removed the
ambiguity by splitting one of affected cages, but I thought you might
like to check it out, just for fun.

In case you are wondering, the shading
of patterned CalcuDokus serves no practical purpose. It’s only
there because it makes them prettier.

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