Book 1 Proposition 1

The markup of the proposition is below:

Let [line AB] be the given finite straight line.
It is required to construct an equilateral triangle on the straight [line AB]. [step]
Describe the [circle BCD] with [center A circle=BCD] and radius [line AB]. [step]
Again describe the [circle ACE] with [center B circle=ACE] and radius [line BA]. [step]
Join the straight lines [line CA] and [line CB] from the [point C] at which the circles cut one another to the points [point A] and [point B]. [step]
Now, since the [point A] is the center of the [circle CDB], therefore [line AC] equals [line AB].
Again, since the [point B] is the center of the [circle CAE], therefore [line BC] equals [line BA].
But [line AC] was proved equal to [line AB], therefore each of the straight lines [line AC] and [line BC] equals [line AB].
And things which equal the same thing also equal one another, therefore [line AC] also equals [line BC].
Therefore the three straight lines [line AC], [line AB], and [line BC] equal one another.
Therefore the [polygon ABC] is equilateral, and it has been constructed on the given finite straight [line AB]. [step]
[clear] [polygon ABC] [step]

[definitions]

[loc A -0.25 0]
[loc B 0.25 0]
[loc C 0 0.433]
[loc D -0.75 0]
[loc E 0.75 0]

This file is saved as postulate1.yc. It is then run through the parser as follows:

python main_parser.py postulate1.yc --output postulate1.html

The postulate1.html file can be open in a browser to create an interactive page that looks as follows:

Hovering over text on the left will highlight the corresponding geometric shapes on the right. Hovering over a geometric shape on the right will highlight the corresponding text on the left. Using the left and right arrow keys will toggle through the steps of the construction.