A short proof of the integrality of the Macdonald (q,t)-Kostka   coefficients
  The Macdonald polynomials can be obtained by acting on the constant 1 with creation operators. Three different expressions for these operators are derived, one from the other, in a rather succint way. When the last of these expressions is used, the formalism is seen to imply straightforwardly the integrality of the (q,t)-Kostka coefficients, that is of the expansion coefficients for the Macdonald functions in terms of Schur functions. 
Luc Lapointe, Luc Vinet