FUNCTION:  InteriorPt - find an interior point of the fundamental chamber
    ,CALLING SEQUENCE:  InteriorPt(R);,    
PARAMETERS:  R = a root system data Structure,SYNOPSIS:   
  InteriorPt(R) returns a point in the interior of the fundamental chamber
  defined by R; i.e., a vector v in the span of Base(R) with the property
  that Iprod(r,v)>0 for all positive roots r. The vector v is chosen so
  that Iprod(r,v)=1 for each simple root r. For crystallographic R, this
  is the same as Weyl[CoRho](R).
  More generally, if S is any list of independent vectors expressed as 
  linear combinations of the standard orthonormal basis e1,e2,...,
  InteriorPt(S) returns the vector v in the linear span of S such that
  Iprod(r,v)=1 for all members r of S.
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   
  InteriorPt(F4);                 yields   e1+2*e2+3*e3+8*e4
  InteriorPt([e1,e2,e1-e3]);      yields        e1+e2,    
SEE ALSO:  Base, Iprod, Structure, Vec2FC, Weyl[CoRho]):
