Scheme PHP [Source Code]
numbered? 
function is_numbered
($aexp)
{return 
    is_atom($aexp) ? is_number($aexp)
    : (   is_eq(car(cdr($aexp)), '+')
       || is_eq(car(cdr($aexp)), 'x')
       || is_eq(car(cdr($aexp)), '^'))
      && is_numbered(car($aexp))
      && is_numbered(car(cdr(cdr($aexp))));
}
value 
function value
($nexp)
{return 
    is_atom($nexp) ? $nexp
    : (is_eq(car(cdr($nexp)), '+') ? 
      plus(value(car($nexp)),
           value(car(cdr(cdr($nexp)))))
      : (is_eq(car(cdr($nexp)), 'x') ? 
          x(value(car($nexp)),
            value(car(cdr(cdr($nexp)))))
        : power(value(car($nexp)),
                value(car(cdr(cdr($nexp)))))));
}
function value
($nexp)
{return 
    is_atom($nexp) ? $nexp
    : (is_eq(operator($nexp), '+') ?
        plus(value(first_sub_exp($nexp)),
             value(second_sub_exp($nexp)))
      : (is_eq(operator($nexp), 'x') ?
          x(value(first_sub_exp($nexp)),
            value(second_sub_exp($nexp)))
        : power(value(first_sub_exp($nexp)),
                value(second_sub_exp($nexp)))));
}
2nd-sub-exp 
function second_sub_exp
($aexp)
{return
    car(cdr(cdr($aexp)));
}
1st-sub-exp 
// prefix
function first_sub_exp
($aexp)
{return 
    car(cdr($aexp));
}
// infix
use function car as first_sub_exp;
operator 
// prefix
use function car as operator;
// infix
function operator
($nexp)
{return 
    car(cdr($nexp));
}
sero? 
function is_sero
($n)
{return
    is_nulll($n);
}
edd1 
function edd1
($n)
{return 
    cons([], $n);
}
zub1 
use function cdr as zub1;
blus 
function blus
($n, $m)
{return 
    is_sero($m) ? $n
    : edd1(blus($n, zub1($m)));
}