\@ifundefined actually defines macros?
31591
loading tocloft makes \ifdefined\chapter TRUE in article class
56892
#if DEBUG vs. Conditional("DEBUG")
87004
Inline functions vs Preprocessor macros
25704
Undefined, unspecified and implementation-defined behavior
13211
babel shorthand "| doesn't work in macros
25478
What does ${1+"$@"} mean in a shell script, and how does it differ from "$@"?
43256
Macro defining macro
45816
What do $< and $@ represent in a Makefile?
88148
Strange behaviour of macros C/C++
142384
Strange error defining a macro with arguments for math mode
93586
Use of # a.k.a. read-macro
66916
Expressions containing globally undefined symbols inside a function where they are defined
108442
C/C++ macro string concatenation
138946
How to define a macro globally in Objective-C?
81447
Defined behaviour for expressions
69632
#define in Java
148104
Defining macros with arguments