Key
    schur
    (schur, List, Matrix)
  Headline
    creates a map between Schur modules
  Usage
    schur(lambda,f)
  Inputs
    lambda:List
      a list of numbers representing a partition
    f:Module
      a map between two free modules
  Outputs 
    F:Matrix
      the result of applying the Schur functor associated to lambda to f
  Description
    Text
      Applies the Schur functor associated to lambda to the map f between free modules.
      The modules @TT "source F"@ and @TT "target F"@ are Schur modules containing 
      certain data in cache (see @TO schurModule@).  
    Example
      R=QQ[x_1,x_2,x_3]
      F=map(R^1,R^3,vars R)
      L=schur({2},F) -- 2nd veronese embedding
      F=matrix{{1_QQ,2,4},{3,9,27},{4,16,64}}
      schur({1,1},F)
      minors(2,F)
      schur({1,1,1},F) == det F
  Caveat
    The partition lambda should be a valid nonempty partition.
  SeeAlso
    schurModule