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I. The function values,/(xi ) = /; (i = 2, 3, ... , n), must be the same in the two splines on either side of Xi at all of the n - I interior points. This constraint yields 2(n - I) conditions.

2. The first derivative of the two splines on either side of point Xi must be equal at all of the n - I interior points. This constraint yields (n - I) conditions.