# Pyramid

## RulesEdit

Enter numbers from 1 to 9 into the cells of the pyramid, so that each number is either the sum or the difference of the two numbers in the cells below. In gray rows, no number may occur twice, while in white rows at least one number does occur twice.

(Rules and example from WPC 2018 IB)

### Rule variationsEdit

- Range of numbers used may vary, as for example 0-9 Pyramid from WPC 2019/World Cup Round 2.

## History of the puzzleEdit

Earliest instance found is "Figure Pyramid" from "varia" round of 2003 Dutch Nationals. The puzzle was written by Hans Eendebak (Netherlands).

## Appearances in the past WPCsEdit

- WPC 2019/Round 2 (Killer) by Erhard Notz
- WPC 2019/World Cup Round 2 (0-9) by Jürgen Blume-Nienhaus
- WPC 2019/World Cup Playoffs by Jürgen Blume-Nienhaus
- WPC 2018/Round 4 (combination) by Jiří Hrdina
- WPC 2018/Round 9 by František Luskač and Jiří Hrdina