1. AlShamary, B., Calin, O., Chang, D.-C.: Global connectivity and optimization on an infinite step distribution. Adv. Appl. Math. 50(4), 634–644 (2013)
2. Calin, O., Chang, D.C.: Sub-Riemannian Geometry, General Theory and Examples, Encyclopedia of Mathematics and its Applications, vol. 126. Cambridge University Press, Cambridge (2009)
3. Calin, O., Chang, D.C.: Geometric Mechanics on Riemannian Manifolds. Applications to Partial Differential Equations, Applied and Numerical Harmonic Analysis. Birkhäuser, Boston Basel Berlin (2004)
4. Calin, O., Chang, D.C.: Non-connectivity example in subRiemannian geometry. Complex Var. Elliptic Equ. 56(1–4), 35–47 (2011)
5. Calin, O., Chang, D.C., Eastwood, M.: Integrability conditions for the Grushin and Martinet distribution. Bull. IMAS New Ser. 8(2), 159–168 (2013)