A doctor and a lawyer were attending a cocktail party when the doctor was approached by a man who asked advice on how to handle his ulcer.
The doctor mumbled some medical advice, then turned to the lawyer and asked,
"How do you handle the situation when you are asked for advice during a social function?"
"Just send a bill for such advice" replied the lawyer.
On the next morning the doctor arrived at his surgery and issued the ulcer-stricken man a $50 bill.
That afternoon he received a $100 bill from the lawyer.
Sudoku is played on a square field 9 by 9 of cells. The field itself is divided into regions (3 by 3 squares).
The goal of Sudoku is to fill all the empty cells with numbers 1-9 (one digit per cell), using the following rules:
1. The number can appear only once in each row.
2. The number can appear only once in each column.
3. The number can appear only once in each district.
Simply put, the same number can appear only once in each row, column and region.