Polynomial valuation : valuation ldegree

valuation or ldegree takes as argument a polynomial given by a symbolic expression or by the list of it's coefficients.
valuation or ldegree returns the valuation of this polynomial, that is the lowest degree of it's non-zero monomials.
Input :

valuation(x^3+x)

Output :

1

Input :

valuation([1,0,1,0])

Output :

1