mathworld.wolfram.com
Unknown
Wolfram MathWorld is a comprehensive online mathematics encyclopedia offering in-depth articles on mathematical concepts, definitions, theorems, formulas, and worked examples. It spans a wide range of topics—from algebra and calculus to geometry and topology—with well-organized entries, diagrams, and references for further exploration.
More resources on Smooth Maps
nLab: Smooth map
Comprehensive entry on smooth maps in higher category theory and topology context
ocw.mit.edu
MIT OpenCourseWare (OCW) provides free, openly licensed MIT course materials. It offers lecture notes, assignments, exams, and sometimes video lectures from a wide range of courses, including mathematics topics relevant to smooth maps.
ncatlab.org
nLab is a collaborative online wiki and reference for higher mathematics (notably category theory, higher algebra, and topology) used by researchers and students. It contains in-depth articles, definitions, and discussions on topics including smooth maps, differential geometry, manifolds, and related concepts.