# Galvagni Figures for Didrafters

## Introduction

A *didrafter* is made by joining two 30°-60°-90°
triangles along equal edges, where the halves of a triangle's hypotenuse
may be used separately.
A didrafter is *proper*
if it can be placed on a polyiamond grid
so all its edges lie on the edges and medians of the grid cells.
Otherwise it is *improper*
or *extended.*
A *Galvagni Figure* for a polydrafter is a polydrafter that can be
tiled with the given polydrafter in more than one way.
Here are some minimal Galvagni Figures
for proper and extended didrafters.

## Galvagni Figures

## Quasi-Galvagni Figures

These figures are not polydrafters, but they can be tiled
by didrafters in more than one way:

## Impossible

Last revised 2017-04-25.

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George Sicherman
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