#GP1(L,n,d): Inputs a list of numbers L and a variable n and a non-neg. d outputs the polynomial of degree d
#P(n), such that P(i)=L[i], for all i from 1 to nops(L). OR FAIL
#nops(L)>=d+2
GP1:=proc(L,n,d) local a,i,P,eq,var:
if nops(L)<d+2 then
 ERROR(`List too short`):
 fi:
#P=a[0]+a[1]*n+...+a[d]*n^d
P:=add(a[i]*n^i,i=0..d):
var:={seq(a[i],i=0..d)}:
eq:={seq(L[i]=subs(n=i,P),i=1..d+2)}:
var:=solve(eq,var):
 if var=NULL then
   RETURN(FAIL):
 fi:
P:=subs(var,P):
if {seq(L[i]-subs(n=i,P),i=d+3..nops(L))}<>{0} then
  RETURN(FAIL):
 fi:
P:
end:



#GP(L,n): Inputs a list of numbers L and a variable n and outputs the polynomial of degree <=nops(L)-2
#P(n), such that P(i)=L[i], for all i from 1 to nops(L). OR FAIL
#nops(L)>=d+2
GP:=proc(L,n) local d,P:
for d from 0 to nops(L)-2 do
 P:=GP1(L,n,d):
 if P<>FAIL then
    RETURN(P):
 fi:
od:
FAIL:
end: