If you can't find a legal copy of the Gilbert text, these highly-regarded textbooks are open-source and free to download:

These add a second operation (multiplication) to the group structure. Examples include integers or polynomials. They help us understand how different types of "numbers" behave when you both add and multiply them.

The study of symmetry. A group is a set with an operation (like addition) that follows specific rules: it must be associative, have an identity element (like zero), and every element must have an inverse.

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by Charles Pinter (Available very cheaply or through many university libraries). To help you get the exact material you need: The specific edition or author (if not Gilbert & Gilbert)

by Thomas Judson (The gold standard for free algebra texts).

Modern algebra isn't just theory; it’s the backbone of (keeping your data safe), Quantum Mechanics , and Coding Theory . It allows mathematicians to prove that certain things—like trisecting an angle with only a compass and straightedge—are physically impossible based on their algebraic structure. Legal Free Alternatives

The most refined structure, where you can add, subtract, multiply, and divide (except by zero). The real numbers ( Rthe real numbers ) and rational numbers ( Qthe rational numbers ) are the classic examples.