Function: setsearch
Section: linear_algebra
C-Name: setsearch
Prototype: lGGD0,L,
Help: setsearch(x,y,{flag=0}): looks if y belongs to the set x. If flag is 0
 or omitted, returns 0 if it is not, otherwise returns the index j such that
 y==x[j]. If flag is non-zero, return 0 if y belongs to x, otherwise the
 index j where it should be inserted

