A Course Of Pure Mathematics G.H.Hardy
A read of this famous undergraduate book was pure joy. The attention here to rigor at such an early stage in the education process is striking.
The first publication of this book. 1908.
This has been a good mental exercise...a plus at my age and in a time of virus.
The author, Hardy had a famous connection with the celebrated Indian mathematician, Ramanujan.
https://en.wikipedia.org/wiki/G_H_Hardy