Unisol

Unisol is a logical puzzle invented by Lawrence Gould that has been printed in the Sydney Morning Herald (Sydney, Australia) and Tele Sept Jeux (Paris, France) since the mid 1980s. It appears in the Sydney Morning Herald on Mondays, Wednesdays and Fridays.

Example

---------------
X | B | E | J | 27 A=5;B=8
---------------
C | D | J | G | 17
---------------
G | E | F | B | 24
---------------
H | A | C | F | 15 --------------- 10 23 23 27 83

Rules

The rules of the puzzle are:
* the letters A to H and J represent the numbers 1 to 9
* each letter may occur only once in a row or column
* seven letters occur twice; two occur only once
* one of the letters that occurs twice has been replaced with an X
* the sums of each row and column and the whole square are given
* the object is to fill in the numbers.

Each puzzle has a unique solution. One of the numbers that occurs twice and one that occurs once are given, though the puzzles are often more interesting to solve without them.

olving Unisols

Things to look for:
* the numbers 1 to 9 add to 45, so the sum of eight letters will give you the value of the ninth
* since seven letters occur twice and two only once the puzzle sums to 90 (2* 1 to 9) minus the sum of the two numbers that occur once
* certain sums can only be made up of certain numbers e.g. a row that adds to 11 must be 1,2,3 & 5
* lines with three letters in common give you the difference between the two other letters
* looking at differences between pairs of letters can give the difference between letters or narrow down possible combinations
* try to find areas where you can combine pieces of information to reduce possibilities.

Mystic Diamond

The Mystic Diamond is a similar puzzle except that the restriction that seven letters occur twice and one of them is X doesn't apply and the diagonal sums are given as well. They are not as interesting a puzzle and there is often more than one solution.