Section 1: Fundamental Concepts

1. (inclusion) $A\subset B$ means that $A$ is a subset of $B$ and includes the case $A=B$ . Sometimes (in other books) they use $\subset$ to indicate proper inclusion (i.e. $A\neq B$ ), for which in this book Munkres uses $\subsetneq$ .
2. (ordered pairs) $(a,b)$ is an ordered pair. Sometimes (in other books) they use $<a,b>$ or other symbols to denote ordered pairs.