function I=tween(a,b)
% tween - all indices in a given range (like interval to set)
%
% tween :: interger, integer -> [[N]->integer].
% tween :: [[2]->interger] -> [[N]->integer].
%
% tween([A,B])=tween(A,B).

if nargin<2, b=a(2); a=a(1); end
if b>=a, I=a:b; else I=a:-1:b; end

