In order to define a free product with amalgamation $A \ast_C B$ you need to define $A,B,C$ and embeddings of $C$ into $A$ and $B$. Alternatively, instead of $C$ you can use a homomorphism $phi: A \rightarrow B$ and its inverse. …
cp's mathem-o-blog
aka CheckMyWorking.com
Interesting Esoterica- Further evidence for addition and numerical competence by a Grey parrot (Psittacus erithacus)
- Orange Peels and Fresnel Integrals
- Passage to the limit in Proposition I, Book I of Newton's Principia
- Tropical Mathematics
- Fractions without Quotients: Arithmetic of Repeating Decimals
- Pantologia. A new (cabinet) cyclopædia, by J.M. Good, O. Gregory, and N. Bosworth assisted by other gentlemen of eminence (Google eBook)
- Nineteen dubious ways to compute the exponential of a matrix, twenty-five years later
- Fibonacci determinants-a combinatorial approach
- Good stories, pity they're not true
- Benjamin Peirce and the Howland will