public boolean declareImmutable(String label, BtrpOperand t) {
        if (isDeclared(label)) {
            return false;
        }
        level.put(label, -1);
        type.put(label, t);
        return true;
    }
public boolean declareImmutable ( String label , BtrpOperand t ) { if ( isDeclared ( label ) ) { return false ; } level . put ( label , - 1 ) ; type . put ( label , t ) ; return true ; }
Declare an immutable variable. The variable must not
has been already declared.

@param label the identifier of the variable
@param t     the operand associated to the identifier
@return {@code true} if the variable as been declared. {@code false} otherwise