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up vote 1 down vote favorite What is a smooth surface in terms of tangents and normals? I read in a book that surfaces are smooth if its surface normals depend continuously on the points of that surface. I did not understand this definition, could somebody simplify it for me? multivariable-calculus surfaces share | cite | improve this question edited Feb 19 '14 at 11:38 Maroon 287 3 13 asked Jul 21 '13 at 19:25 sagar 11 1 2