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

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