I have studied both single variable and multivariable calculus. I was younger and spent hardly anytime on them but did fairly well at the university level. I regret now that I did not master the subjects as I have an intense passion to learn ODE's. Do you think I should start studying Tenenbaum/Pollard without re-learning calculus? I feel that if I get stuck on some parts that require tricky integration or some other concept I can relearn it then. I understand Calculus. But my technique is rusty and there are holes in my knowledge. What do you suggest? Should I start delving into diff equations?