The Eureka notation system is a compact method to write Alternating Inference Chains.
Candidate digits are written as a prefix to the cell, with the digit number in parenthesis. This is the way to write candidate for digit 1 in the cell at row 5 and column 4.
Weak links are represented by a dash.
Strong links are represented by an equal sign.
There is no need to repeat the cell name when multiple candidates of that cell are used in the chain. A link between 2 candidates in a single cell is placed inside the parenthesis.
When groups of cells are used in the chain, they are named in the most efficient way.
- All cells belong to a single row
- All cells belong to a single column
- Unordered group, in a box
When all candidates represent the same digit, this digit can be placed before the entire chain as a prefix.
When an embedded ALS is part of the chain, the digit linked to the previous node is isolated from the remaining digits with a strong link symbol. The remaining digits are placed in such an order that the digit linked to the next node is the last one.
When read from left to right, the chain must contain alternating strong and weak links. There can be no 2 adjacent dashes or equal signs, whether or not they are placed inside the parenthesis.
The result is placed after the chain, separated by a double arrow.
(1)r5c4-(1=4)r5c8-(4)r9c8=(4-1)r7c7=(1)r7c4-(1)r5c4 => r5c4<>1