Function still_valued 

fn still_valued(leg: &Leg, coupon: &AnyCoupon, valuation: NaiveDate) -> bool

Whether a valuation on valuation still values coupon of leg, and so still reads its resets. A non-summing leg pays once: every coupon counts until that payment and none after (Leg::npv). A summing leg skips a coupon paid on or before the valuation date (Leg::walk).