public boolean addUsedPrefix(String prefix){
  prefix=prefix.replace(' ','_');
  return usedPrefixes.add(prefix.intern());
}

public boolean addUsedPrefix ( String prefix ) { prefix = prefix . replace ( ' ' , '_' ) ; return usedPrefixes . add ( prefix . intern ( ) ) ; }
changes ' ' characters to ' _ ' , and then tries to add it to the used prefix list . returns true if successful .
