Function: serchop
Section: conversions
C-Name: serchop
Prototype: GD0,L,
Help: serchop(s,{n=0}): remove all terms of degree strictly less than n in
 series s.
Doc: remove all terms of degree strictly less than $n$ in series $s$. When
 the series contains no terms of degree $< n$, return $O(x^n)$.
 \bprog
 ? s = 1/x + x + 2*x^2 + O(x^3);
 ? serchop(s)
 %2 = x + 2*x^3 + O(x^3)
 ? serchop(s, 2)
 %3 = 2*x^2 + O(x^3)
 ? serchop(s, 100)
 %4 = O(x^100)
 @eprog
