public boolean remove(Variable v) {
    if (immutable) throw new IllegalStateException("Cant modify");
    return v != null && variables.remove(v);
  }
public boolean remove ( Variable v ) { if ( immutable ) throw new IllegalStateException ( "Cant modify" ) ; return v != null && variables . remove ( v ) ; }
Remove a Variable : uses the variable hashCode to find it.

@param v remove this Variable.
@return true if was found and removed