* Can the manifold be "flattened out"? Any piece of spaghetti can be made straight, and yet an orange peel cannot be flattened without tearing. How can we tell if it is possible to flatten a given surface? This question leads to the study of ''curvature''. | * Can the manifold be "flattened out"? Any piece of spaghetti can be made straight, and yet an orange peel cannot be flattened without tearing. How can we tell if it is possible to flatten a given surface? This question leads to the study of ''curvature''. |