PolynomialQ
PolynomialQ[expr, var] yields True if expr is a polynomial in var, and yields False otherwise. PolynomialQ[expr, , ... ] tests whether expr is a polynomial in the .
The need not be symbols; PolynomialQ[f[a] + f[a]^2, f[a]] . See The Mathematica Book: Section 2.3.5 and Section 3.3.2. See also: Collect, Series.
Further Examples
PolynomialQ[expr, var] yields True if expr is a polynomial in var, and yields False otherwise. 
, ... 
] tests whether expr is a polynomial in the 
. 
need not be symbols; PolynomialQ[f[a] + f[a]^2, f[a]] 
. 
