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Continue to ChatOn Parallel Surfaces of Ruled Surfaces with Null Rulings - https://avesis.ogu.edu.tr/publication/details/58c3f4cf-c138-4814-8709-23248a82365e/on-parallel-surfaces-of-ruled-surfaces-with-null-rulings
On Parallel Surfaces of Ruled Surfaces with Null Rulings - https://avesis.ogu.edu.tr/publication/details/58c3f4cf-c138-4814-8709-23248a82365e/on-parallel-surfaces-of-ruled-surfaces-with-null-rulings