algebraic topology - Comparison between Van Kampen theorem from Allen Hatcher and "Introduction to knot theory". - Mathematics Stack Exchange
Seifert–Van Kampen theorem - Wikipedia
What is...the Seifert–Van Kampen theorem? Or: Cut and compute
at.algebraic topology - Connection between Stalling's end theorem and Seifert-van Kampen Theorem - MathOverflow
The Seifert-van Kampen Theorem Example 1 - Mathonline
algebraic topology - On a Remark on the van Kampen theorem in Rolfsen's Knots and Links - Mathematics Stack Exchange
Algebraic Topology: Seifert Van Kampen Theorem, part 1
SOLVED: The Seifert-van Kampen Theorem carries N to the identity element; that it induces a homomorphism G1/N (G1 * G2)/N. Similarly, the composite of the inclusion and projection homomorphisms induces a homomorphism
PDF) A Seifert-Van Kampen theorem in non-abelian algebra
The Seifert-van Kampen Theorem in Homotopy Type Theory