// so node is the result.  Is it exact?

		// (It's tempting to put this condition before the
		// child loop, but it gives the wrong result in the
		// case where a node (e.g. ExprStmt) and its sole
		// child have equal intervals.)
		if start == nodePos && end == nodeEnd {
			return true // exact match
		}

		return false // inexact: overlaps multiple children
	}

	// if there is an interface, the other type must implement the
	// interface.
	exact
)

func (m unifyMode) String() string {
	switch m {
	case 0:
		return "inexact"
	case assign:
		return "assign"
	case exact:
		return "exact"
	case assign | exact:
		return "assign, exact"
	}
	return fmt.Sprintf("mode %d", m)
}

	// if there is an interface, the other type must implement the
	// interface.
	exact
)

func (m unifyMode) String() string {
	switch m {
	case 0:
		return "inexact"
	case assign:
		return "assign"
	case exact:
		return "exact"
	case assign | exact:
		return "assign, exact"
	}
	return fmt.Sprintf("mode %d", m)
}

	if x < 0.25 {
		return -Sin(Pi * x)
	}

	// argument reduction
	z := Floor(x)
	var n int
	if z != x { // inexact
		x = Mod(x, 2)
		n = int(x * 4)
	} else {
		if x >= Two53 { // x must be even
			x = 0
			n = 0
		} else {
			if x < Two52 {
				z = x + Two52 // exact
			}
			n = int(1 & Float64bits(z))
			x = float64(n)
			n <<= 2
		}
	}
	switch n {
	case 0:

//              |R1/S1 - f(x)|  < 2**(-62.57)
//              |R2/S2 - f(x)|  < 2**(-61.52)
//
//      5. For inf > x >= 28
//              erf(x)  = sign(x) *(1 - tiny)  (raise inexact)
//              erfc(x) = tiny*tiny (raise underflow) if x > 0
//                      = 2 - tiny if x<0
//
//      7. Special case:
//              erf(0)  = 0, erf(inf)  = 1, erf(-inf) = -1,

		} else {
			u := pone(x)
			v := qone(x)
			z = (1 / SqrtPi) * (u*cc - v*ss) / Sqrt(x)
		}
		if sign {
			return -z
		}
		return z
	}
	if x < TwoM27 { // |x|<2**-27
		return 0.5 * x // inexact if x!=0 necessary
	}
	z := x * x
	r := z * (R00 + z*(R01+z*(R02+z*R03)))
	s := 1.0 + z*(S01+z*(S02+z*(S03+z*(S04+z*S05))))
	r *= x
	z = 0.5*x + r/s
	if sign {
		return -z
	}
	return z
}

// entirely in floating-point math, do so, avoiding the expense of decimalToFloatBits.
// Three common cases:
//
//	value is exact integer
//	value is exact integer * exact power of ten
//	value is exact integer / exact power of ten
//
// These all produce potentially inexact but correctly rounded answers.
func atof64exact(mantissa uint64, exp int, neg bool) (f float64, ok bool) {
	if mantissa>>float64info.mantbits != 0 {

func (q *Quantity) RoundUp(scale Scale) bool {
	if q.d.Dec != nil {
		q.s = ""
		d, exact := q.d.AsScale(scale)
		q.d = d
		return exact
	}
	// avoid clearing the string value if we have already calculated it
	if q.i.scale >= scale {
		return true
	}
	q.s = ""
	i, exact := q.i.AsScale(scale)
	q.i = i
	return exact
}

// Add adds the provide y quantity to the current value. If the current value is zero,

		if x.neg {
			var z float64
			return -z, Exact
		}
		return 0.0, Exact

	case inf:
		if x.neg {
			return math.Inf(-1), Exact
		}
		return math.Inf(+1), Exact
	}

	panic("unreachable")
}

// Int returns the result of truncating x towards zero;
// or nil if x is an infinity.
// The result is [Exact] if x.IsInt(); otherwise it is [Below]

                    stringMatch:
                      exact: rule[0]-to[0]-method[1]
                - header:
                    name: :method
                    stringMatch:
                      exact: rule[0]-to[0]-method[2]
            - orRules:
                rules:
                - urlPath:
                    path:
                      exact: rule[0]-to[0]-path[1]
                - urlPath: